diff --git a/composer.json b/composer.json
index 9f12640..2f42660 100644
--- a/composer.json
+++ b/composer.json
@@ -25,19 +25,23 @@
     },
     "autoload-dev": {
         "psr-4": {
-            "Tests\\": "tests/"
+            "Welp\\MailchimpBundle\\Tests\\": "tests/"
         }
     },
     "require": {
-        "php": ">=5.6",
-        "drewm/mailchimp-api": "2.5.*"
+        "php": ">=8.1",
+        "drewm/mailchimp-api": "^2.5",
+        "symfony/event-dispatcher": "^6.3||^7.0",
+        "symfony/framework-bundle": "^6.3||^7.0"
     },
     "require-dev": {
-        "phpspec/phpspec": "~2@dev",
-        "phpunit/phpunit": "~5",
-        "symfony/symfony": ">=2.7"
+        "phpspec/phpspec": "^7.5",
+        "phpunit/phpunit": "^9.6",
+        "symfony/symfony": "^6.3||^7.0"
     },
     "config": {
-        "bin-dir": "bin"
+        "bin-dir": "bin",
+        "preferred-install": "dist",
+        "sort-packages": true
     }
 }
diff --git a/config/routes.yaml b/config/routes.yaml
new file mode 100644
index 0000000..514d848
--- /dev/null
+++ b/config/routes.yaml
@@ -0,0 +1,3 @@
+welp_mailchimp_webhook:
+    resource: '../src/Controller'
+    type:     attribute
\ No newline at end of file
diff --git a/src/Resources/config/services.yml b/config/services.yaml
similarity index 95%
rename from src/Resources/config/services.yml
rename to config/services.yaml
index 7aac2bc..d9c9959 100644
--- a/src/Resources/config/services.yml
+++ b/config/services.yaml
@@ -6,6 +6,13 @@ parameters:
     welp_mailchimp.config_list_provider_class: Welp\MailchimpBundle\Provider\ConfigListProvider
 
 services:
+    _defaults:
+        autowire: true
+        autoconfigure: true
+
+    Welp\MailchimpBundle\Controller\:
+        resource: '../src/Controller/*'
+
     # MailChimp
     welp_mailchimp.mailchimp_master:
         class: DrewM\MailChimp\MailChimp
diff --git a/src/Command/SynchronizeMergeFieldsCommand.php b/src/Command/SynchronizeMergeFieldsCommand.php
index 4c80468..fe79ca5 100644
--- a/src/Command/SynchronizeMergeFieldsCommand.php
+++ b/src/Command/SynchronizeMergeFieldsCommand.php
@@ -15,14 +15,14 @@ class SynchronizeMergeFieldsCommand extends Command
      *
      * @var ListSynchronizer
      */
-    private $listSynchronizer;
+    private ListSynchronizer $listSynchronizer;
 
     /**
      * The configured list provider.
      *
      * @var ListProviderInterface
      */
-    private $listProvider;
+    private ListProviderInterface $listProvider;
 
     public function __construct(ListSynchronizer $listSynchronizer, ListProviderInterface $listProvider)
     {
@@ -32,7 +32,7 @@ public function __construct(ListSynchronizer $listSynchronizer, ListProviderInte
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setDescription('Synchronizing merge fields in MailChimp')
@@ -41,7 +41,7 @@ protected function configure()
         ;
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $output->writeln(sprintf('<info>%s</info>', $this->getDescription()));
 
@@ -50,5 +50,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         foreach ($lists as $list) {
             $this->listSynchronizer->synchronizeMergeFields($list->getListId(), $list->getMergeFields());
         }
+
+        return Command::SUCCESS;
     }
 }
diff --git a/src/Command/SynchronizeSubscribersCommand.php b/src/Command/SynchronizeSubscribersCommand.php
index a71c88b..822c931 100644
--- a/src/Command/SynchronizeSubscribersCommand.php
+++ b/src/Command/SynchronizeSubscribersCommand.php
@@ -17,21 +17,21 @@ class SynchronizeSubscribersCommand extends Command
      *
      * @var ListSynchronizer
      */
-    private $listSynchronizer;
+    private ListSynchronizer $listSynchronizer;
 
     /**
      * The configured list provider.
      *
      * @var ListProviderInterface
      */
-    private $listProvider;
+    private ListProviderInterface $listProvider;
 
     /**
      * Mailchimp API class.
      *
      * @var MailChimp
      */
-    private $mailchimp;
+    private MailChimp $mailchimp;
 
     public function __construct(ListSynchronizer $listSynchronizer, ListProviderInterface $listProvider, MailChimp $mailchimp)
     {
@@ -45,7 +45,7 @@ public function __construct(ListSynchronizer $listSynchronizer, ListProviderInte
     /**
      * {@inheritdoc}
      */
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setDescription('Synchronizing subscribers in MailChimp')
@@ -63,7 +63,7 @@ protected function configure()
     /**
      * {@inheritdoc}
      */
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $output->writeln(sprintf('<info>%s</info>', $this->getDescription()));
 
@@ -72,16 +72,21 @@ protected function execute(InputInterface $input, OutputInterface $output)
         foreach ($lists as $list) {
             $output->writeln(sprintf('Synchronize list %s', $list->getListId()));
             $batchesResult = $this->listSynchronizer->synchronize($list);
+
             if ($input->getOption('follow-sync')) {
                 while (!$this->batchesFinished($batchesResult)) {
                     $batchesResult = $this->refreshBatchesResult($batchesResult);
+
                     foreach ($batchesResult as $key => $batch) {
                         $output->writeln($this->displayBatchInfo($batch));
                     }
+
                     sleep(2);
                 }
             }
         }
+
+        return Command::SUCCESS;
     }
 
     /**
@@ -91,13 +96,13 @@ protected function execute(InputInterface $input, OutputInterface $output)
      *
      * @return array
      */
-    private function refreshBatchesResult($batchesResult)
+    private function refreshBatchesResult(array $batchesResult): array
     {
         $refreshedBatchsResults = [];
 
         foreach ($batchesResult as $key => $batch) {
             $batch = $this->mailchimp->get('batches/'.$batch['id']);
-            array_push($refreshedBatchsResults, $batch);
+            $refreshedBatchsResults[] = $batch;
         }
 
         return $refreshedBatchsResults;
@@ -110,11 +115,11 @@ private function refreshBatchesResult($batchesResult)
      *
      * @return bool
      */
-    private function batchesFinished($batchesResult)
+    private function batchesFinished(array $batchesResult): bool
     {
         $allfinished = true;
         foreach ($batchesResult as $key => $batch) {
-            if ('finished' != $batch['status']) {
+            if ('finished' !== $batch['status']) {
                 $allfinished = false;
             }
         }
@@ -129,9 +134,9 @@ private function batchesFinished($batchesResult)
      *
      * @return string
      */
-    private function displayBatchInfo($batch)
+    private function displayBatchInfo(array $batch): string
     {
-        if ('finished' == $batch['status']) {
+        if ('finished' === $batch['status']) {
             return sprintf('batch %s is finished, operations %d/%d with %d errors. http responses: %s', $batch['id'], $batch['finished_operations'], $batch['total_operations'], $batch['errored_operations'], $batch['response_body_url']);
         }
 
diff --git a/src/Command/WebhookCommand.php b/src/Command/WebhookCommand.php
index 7b42e16..59a677a 100644
--- a/src/Command/WebhookCommand.php
+++ b/src/Command/WebhookCommand.php
@@ -15,14 +15,14 @@ class WebhookCommand extends Command
      *
      * @var ListProviderInterface
      */
-    private $listProvider;
+    private ListProviderInterface $listProvider;
 
     /**
      * The configured list repository.
      *
      * @var ListRepository
      */
-    private $listRepository;
+    private ListRepository $listRepository;
 
     public function __construct(ListProviderInterface $listProvider, ListRepository $listRepository)
     {
@@ -32,7 +32,7 @@ public function __construct(ListProviderInterface $listProvider, ListRepository
         parent::__construct();
     }
 
-    protected function configure()
+    protected function configure(): void
     {
         $this
             ->setDescription('Add main webhook to a MailChimp List')
@@ -41,7 +41,7 @@ protected function configure()
         // @TODO add params : listId, webhookurl
     }
 
-    protected function execute(InputInterface $input, OutputInterface $output)
+    protected function execute(InputInterface $input, OutputInterface $output): int
     {
         $output->writeln(sprintf('<info>%s</info>', $this->getDescription()));
 
@@ -56,5 +56,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         }
 
         $output->writeln('✔ done');
+
+        return Command::SUCCESS;
     }
 }
diff --git a/src/Controller/WebhookController.php b/src/Controller/WebhookController.php
index a0e2809..b859ad1 100644
--- a/src/Controller/WebhookController.php
+++ b/src/Controller/WebhookController.php
@@ -2,34 +2,33 @@
 
 namespace Welp\MailchimpBundle\Controller;
 
-use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
-use Sensio\Bundle\FrameworkExtraBundle\Configuration\Method;
-use Symfony\Bundle\FrameworkBundle\Controller\Controller;
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\DependencyInjection\Attribute\Autowire;
+use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\Request;
-use Symfony\Component\HttpKernel\Exception\AccessDeniedHttpException;
-
+use Symfony\Component\Routing\Annotation\Route; // @TODO: deprecated since Symfony 6.4/7.0
 use Welp\MailchimpBundle\Provider\ListProviderInterface;
 use Welp\MailchimpBundle\Event\WebhookEvent;
 
-/**
- * @Route("/webhook")
- */
-class WebhookController extends Controller
+#[Route('/webhook')]
+class WebhookController extends AbstractController
 {
 
     /**
      * Endpoint for the mailchimp list Webhook
      * https://apidocs.mailchimp.com/webhooks/
-     * @Route("/endpoint", name="webhook_index")
-     * @Method({"POST", "GET"})
      * @param Request $request
-     * @throws AccessDeniedHttpException
+     * @param EventDispatcherInterface $eventDispatcher
      * @return JsonResponse
      */
-    public function indexAction(Request $request)
+    #[Route('/endpoint', name: 'webhook_index')]
+    public function indexAction(
+        Request $request,
+        EventDispatcherInterface $eventDispatcher,
+        #[Autowire('@welp_mailchimp.list_provider')] $listProvider,
+    ): JsonResponse
     {
-
         // For Mailchimp ping GET
         if ($request->isMethod('GET')) {
             return new JsonResponse([
@@ -37,10 +36,9 @@ public function indexAction(Request $request)
                 'ping' => 'pong',
             ]);
         }
-
         // Handle POST request of Mailchimp
         $type = $request->request->get('type');
-        $data = $request->request->get('data');
+        $data = $request->request->all('data'); // all() returns an array
         /* Response example:
             data[merges][FNAME]: Tztz
             data[merges][EMAIL]: tztz@gmail.com
@@ -55,64 +53,39 @@ public function indexAction(Request $request)
         $hooksecret = $request->query->get('hooksecret');
 
         if (empty($type) || empty($data) || empty($hooksecret) || !array_key_exists('list_id', $data)) {
-            throw new AccessDeniedHttpException('incorrect data format!');
+            throw $this->createAccessDeniedException('Incorrect data format!');
         }
 
         $listId = $data['list_id'];
 
-        $listProviderKey = $this->getParameter('welp_mailchimp.list_provider');
-        try {
-            $listProvider = $this->get($listProviderKey); 
-        } catch (ServiceNotFoundException $e) {
-            throw new \InvalidArgumentException(sprintf('List Provider "%s" should be defined as a service.', $listProviderKey), $e->getCode(), $e);
-        }
-
         if (!$listProvider instanceof ListProviderInterface) {
-            throw new \InvalidArgumentException(sprintf('List Provider "%s" should implement Welp\MailchimpBundle\Provider\ListProviderInterface.', $listProviderKey));
+            throw new \InvalidArgumentException(sprintf('List Provider "%s" should implement Welp\MailchimpBundle\Provider\ListProviderInterface.', $listProvider::class));
         }
 
         $list = $listProvider->getList($listId);
 
         // Check the webhook_secret
         $authorized = false;
-        if($list != null && $list->getWebhookSecret() == $hooksecret) {
+
+        if ($list !== null && $list->getWebhookSecret() === $hooksecret) {
             $authorized = true;                           
         }
 
         if (!$authorized) {
-            throw new AccessDeniedHttpException('Webhook secret mismatch!');
+            throw $this->createAccessDeniedException('Webhook secret mismatch!');
         }
 
-        // Trigger the right event
-        switch ($type) {
-            case 'subscribe':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_SUBSCRIBE, new WebhookEvent($data));
-                break;
-            case 'unsubscribe':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_UNSUBSCRIBE, new WebhookEvent($data));
-                break;
-            case 'profile':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_PROFILE, new WebhookEvent($data));
-                break;
-            case 'cleaned':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_CLEANED, new WebhookEvent($data));
-                break;
-            case 'upemail':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_UPEMAIL, new WebhookEvent($data));
-                break;
-            case 'campaign':
-                $dispatcher = $this->get('event_dispatcher');
-                $dispatcher->dispatch(WebhookEvent::EVENT_CAMPAIGN, new WebhookEvent($data));
-                break;
-            default:
-                throw new AccessDeniedHttpException('type mismatch!');
-                break;
-        }
+        $eventName = match ($type) {
+            'subscribe' => WebhookEvent::EVENT_SUBSCRIBE,
+            'unsubscribe' => WebhookEvent::EVENT_UNSUBSCRIBE,
+            'profile' => WebhookEvent::EVENT_PROFILE,
+            'cleaned' => WebhookEvent::EVENT_CLEANED,
+            'upemail' => WebhookEvent::EVENT_UPEMAIL,
+            'campaign' => WebhookEvent::EVENT_CAMPAIGN,
+            default => throw $this->createAccessDeniedException('Type mismatch!'),
+        };
+
+        $eventDispatcher->dispatch(new WebhookEvent($data), $eventName);
 
         return new JsonResponse([
             'type' => $type,
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
index 0cc8a99..3e9bc4e 100644
--- a/src/DependencyInjection/Configuration.php
+++ b/src/DependencyInjection/Configuration.php
@@ -15,17 +15,12 @@ class Configuration implements ConfigurationInterface
     /**
      * {@inheritDoc}
      */
-    public function getConfigTreeBuilder()
+    public function getConfigTreeBuilder(): TreeBuilder
     {
         $treeBuilder = new TreeBuilder('welp_mailchimp');
 
-        if (method_exists($treeBuilder, 'getRootNode')) {
-            $rootNode = $treeBuilder->getRootNode();
-        } else {
-            $rootNode = $treeBuilder->root('welp_mailchimp');
-        }
-
-        $rootNode
+        $treeBuilder
+            ->getRootNode()
             ->children()
                 ->scalarNode('api_key')
                     ->isRequired()
diff --git a/src/DependencyInjection/WelpMailchimpExtension.php b/src/DependencyInjection/WelpMailchimpExtension.php
index 72c3a2e..69081ff 100644
--- a/src/DependencyInjection/WelpMailchimpExtension.php
+++ b/src/DependencyInjection/WelpMailchimpExtension.php
@@ -4,13 +4,13 @@
 
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
-use Symfony\Component\DependencyInjection\Loader;
+use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 
 class WelpMailchimpExtension extends Extension
 {
-    public function load(array $configs, ContainerBuilder $container)
+    public function load(array $configs, ContainerBuilder $container): void
     {
         $configuration = new Configuration();
         $config = $this->processConfiguration($configuration, $configs);
@@ -19,8 +19,8 @@ public function load(array $configs, ContainerBuilder $container)
         $container->setParameter('welp_mailchimp.list_provider', $config['list_provider']);
         $container->setParameter('welp_mailchimp.api_key', isset($config['api_key']) ? $config['api_key'] : null);
 
-        $loader = new Loader\YamlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
-        $loader->load('services.yml');
+        $loader = new YamlFileLoader($container, new FileLocator(__DIR__ . '/../../config'));
+        $loader->load('services.yaml');
 
         // create an alias for the chosen list provider service
         $alias = $config['list_provider'];
@@ -35,9 +35,10 @@ public function getAlias(): string
         return 'welp_mailchimp';
     }
 
-    public function loadSubscriberProviders(ContainerBuilder $container, $lists)
+    public function loadSubscriberProviders(ContainerBuilder $container, $lists): void
     {
         $providerFactory = $container->getDefinition('welp_mailchimp.provider.factory');
+
         foreach ($lists as $list) {
             $providerKey = $list['subscriber_provider'];
             $providerFactory->addMethodCall('addProvider', [$providerKey, new Reference($providerKey)]);
diff --git a/src/Event/SubscriberEvent.php b/src/Event/SubscriberEvent.php
index 68934f4..5587347 100644
--- a/src/Event/SubscriberEvent.php
+++ b/src/Event/SubscriberEvent.php
@@ -2,7 +2,7 @@
 
 namespace Welp\MailchimpBundle\Event;
 
-use Symfony\Component\EventDispatcher\Event;
+use Symfony\Contracts\EventDispatcher\Event;
 use Welp\MailchimpBundle\Subscriber\Subscriber;
 
 /**
@@ -14,69 +14,69 @@ class SubscriberEvent extends Event
      * Event to subscribe a User
      * @var string
      */
-    const EVENT_SUBSCRIBE = 'welp.mailchimp.subscribe';
+    public const EVENT_SUBSCRIBE = 'welp.mailchimp.subscribe';
 
     /**
      * Event to unsubscribe a User
      * @var string
      */
-    const EVENT_UNSUBSCRIBE = 'welp.mailchimp.unsubscribe';
+    public const EVENT_UNSUBSCRIBE = 'welp.mailchimp.unsubscribe';
 
     /**
      * Event to pending a User
      * @var string
      */
-    const EVENT_PENDING = 'welp.mailchimp.pending';
+    public const EVENT_PENDING = 'welp.mailchimp.pending';
 
     /**
      * Event to clean a User
      * @var string
      */
-    const EVENT_CLEAN = 'welp.mailchimp.clean';
+    public const EVENT_CLEAN = 'welp.mailchimp.clean';
 
     /**
      * Event to update a User
      * @var string
      */
-    const EVENT_UPDATE = 'welp.mailchimp.update';
+    public const EVENT_UPDATE = 'welp.mailchimp.update';
 
     /**
      * Event to change email of a User
      * @var string
      */
-    const EVENT_CHANGE_EMAIL = 'welp.mailchimp.change_email';
+    public const EVENT_CHANGE_EMAIL = 'welp.mailchimp.change_email';
 
     /**
      * Event to delete a User
      * @var string
      */
-    const EVENT_DELETE = 'welp.mailchimp.delete';
+    public const EVENT_DELETE = 'welp.mailchimp.delete';
 
     /**
      * MailChimp ListId
      * @var string
      */
-    protected $listId;
+    protected string $listId;
 
     /**
      * User as Subscriber
      * @var Subscriber
      */
-    protected $subscriber;
+    protected Subscriber $subscriber;
 
     /**
      * Subscriber's oldEmail (used for EVENT_CHANGE_EMAIL)
      * @var string
      */
-    protected $oldEmail;
+    protected ?string $oldEmail;
 
     /**
      *
-     * @param string     $listId
+     * @param string $listId
      * @param Subscriber $subscriber
-     * @param string     $oldEmail
+     * @param string|null $oldEmail
      */
-    public function __construct($listId, Subscriber $subscriber, $oldEmail = null)
+    public function __construct(string $listId, Subscriber $subscriber, ?string $oldEmail = null)
     {
         $this->listId = $listId;
         $this->subscriber = $subscriber;
@@ -87,7 +87,7 @@ public function __construct($listId, Subscriber $subscriber, $oldEmail = null)
      * Get MailChimp listId
      * @return string
      */
-    public function getListId()
+    public function getListId(): string
     {
         return $this->listId;
     }
@@ -96,16 +96,16 @@ public function getListId()
      * Get the User as Subscriber
      * @return Subscriber
      */
-    public function getSubscriber()
+    public function getSubscriber(): Subscriber
     {
         return $this->subscriber;
     }
 
     /**
      * Get Subscriber's oldEmail (used for EVENT_CHANGE_EMAIL)
-     * @return string
+     * @return string|null
      */
-    public function getOldEmail()
+    public function getOldEmail(): ?string
     {
         return $this->oldEmail;
     }
diff --git a/src/Event/SubscriberListener.php b/src/Event/SubscriberListener.php
index c6c8663..bb5a380 100644
--- a/src/Event/SubscriberListener.php
+++ b/src/Event/SubscriberListener.php
@@ -2,18 +2,18 @@
 
 namespace Welp\MailchimpBundle\Event;
 
+use Symfony\Contracts\EventDispatcher\Event;
 use Welp\MailchimpBundle\Subscriber\ListRepository;
-use Welp\MailchimpBundle\Event\SubscriberEvent;
 
 /**
  * Listener for subscriber unit synchronization
  */
-class SubscriberListener
+class SubscriberListener extends Event
 {
     /**
      * @var ListRepository
      */
-    protected $listRepository;
+    protected ListRepository $listRepository;
 
     /**
      * @param ListRepository $listRepository
@@ -28,7 +28,7 @@ public function __construct(ListRepository $listRepository)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onSubscribe(SubscriberEvent $event)
+    public function onSubscribe(SubscriberEvent $event): void
     {
         $this->listRepository->subscribe(
             $event->getListId(),
@@ -41,7 +41,7 @@ public function onSubscribe(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onUnsubscribe(SubscriberEvent $event)
+    public function onUnsubscribe(SubscriberEvent $event): void
     {
         $this->listRepository->unsubscribe(
             $event->getListId(),
@@ -54,7 +54,7 @@ public function onUnsubscribe(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onPending(SubscriberEvent $event)
+    public function onPending(SubscriberEvent $event): void
     {
         $this->listRepository->pending(
             $event->getListId(),
@@ -67,7 +67,7 @@ public function onPending(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onClean(SubscriberEvent $event)
+    public function onClean(SubscriberEvent $event): void
     {
         $this->listRepository->clean(
             $event->getListId(),
@@ -80,7 +80,7 @@ public function onClean(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onUpdate(SubscriberEvent $event)
+    public function onUpdate(SubscriberEvent $event): void
     {
         $this->listRepository->update(
             $event->getListId(),
@@ -93,7 +93,7 @@ public function onUpdate(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onChangeEmail(SubscriberEvent $event)
+    public function onChangeEmail(SubscriberEvent $event): void
     {
         $this->listRepository->changeEmailAddress(
             $event->getListId(),
@@ -107,7 +107,7 @@ public function onChangeEmail(SubscriberEvent $event)
      * @param  SubscriberEvent $event
      * @return void
      */
-    public function onDelete(SubscriberEvent $event)
+    public function onDelete(SubscriberEvent $event): void
     {
         $this->listRepository->delete(
             $event->getListId(),
diff --git a/src/Event/WebhookEvent.php b/src/Event/WebhookEvent.php
index 8f808d5..a75cca2 100644
--- a/src/Event/WebhookEvent.php
+++ b/src/Event/WebhookEvent.php
@@ -2,7 +2,7 @@
 
 namespace Welp\MailchimpBundle\Event;
 
-use Symfony\Component\EventDispatcher\Event;
+use Symfony\Contracts\EventDispatcher\Event;
 
 /**
  * Event for MailChimp webhook
@@ -13,44 +13,44 @@ class WebhookEvent extends Event
      * Event triggered when received webhook for user subscribe
      * @var string
      */
-    const EVENT_SUBSCRIBE = 'welp.mailchimp.webhook.subscribe';
+    public const EVENT_SUBSCRIBE = 'welp.mailchimp.webhook.subscribe';
     /**
      * Event triggered when received webhook for user unsubscribe
      * @var string
      */
-    const EVENT_UNSUBSCRIBE = 'welp.mailchimp.webhook.unsubscribe';
+    public const EVENT_UNSUBSCRIBE = 'welp.mailchimp.webhook.unsubscribe';
     /**
      * Event triggered when received webhook for user update profile
      * @var string
      */
-    const EVENT_PROFILE = 'welp.mailchimp.webhook.profile';
+    public const EVENT_PROFILE = 'welp.mailchimp.webhook.profile';
     /**
      * Event triggered when received webhook for user cleaned
      * @var string
      */
-    const EVENT_CLEANED = 'welp.mailchimp.webhook.cleaned';
+    public const EVENT_CLEANED = 'welp.mailchimp.webhook.cleaned';
     /**
      * Event triggered when received webhook for user update email [legacy?]
      * @var string
      */
-    const EVENT_UPEMAIL = 'welp.mailchimp.webhook.upemail';
+    public const EVENT_UPEMAIL = 'welp.mailchimp.webhook.upemail';
     /**
      * Event triggered when received webhook for new campaign send
      * @var string
      */
-    const EVENT_CAMPAIGN = 'welp.mailchimp.webhook.campaign';
+    public const EVENT_CAMPAIGN = 'welp.mailchimp.webhook.campaign';
 
     /**
      * Data form webhook request
      * @var array
      */
-    protected $data;
+    protected array $data;
 
     /**
      *
      * @param array $data
      */
-    public function __construct($data)
+    public function __construct(array $data)
     {
         $this->data = $data;
     }
@@ -59,7 +59,7 @@ public function __construct($data)
      * Get data form webhook request
      * @return array
      */
-    public function getData()
+    public function getData(): array
     {
         return $this->data;
     }
diff --git a/src/Exception/MailchimpException.php b/src/Exception/MailchimpException.php
index c4a9416..b007310 100644
--- a/src/Exception/MailchimpException.php
+++ b/src/Exception/MailchimpException.php
@@ -12,20 +12,20 @@ class MailchimpException extends \Exception
      * for this occurrence of the problem.
      * @var int
      */
-    private $status;
+    private int $status;
 
     /**
      * A human-readable explanation specific to this occurrence of the problem.
      * @var string
      */
-    private $detail;
+    private string $detail;
 
     /**
      * An absolute URI that identifies the problem type. When dereferenced,
      * it should provide human-readable documentation for the problem type.
      * @var string
      */
-    private $type;
+    private string $type;
 
     /**
      * A short, human-readable summary of the problem type.
@@ -33,20 +33,20 @@ class MailchimpException extends \Exception
      * except for purposes of localization.
      * @var string
      */
-    private $title;
+    private string $title;
 
     /**
      * For field-specific details, see the 'errors' array.
-     * @var array
+     * @var array|null
      */
-    private $errors;
+    private ?array $errors;
 
     /**
      * A string that identifies this specific occurrence of the problem.
      * Please provide this ID when contacting support.
      * @var string
      */
-    private $instance;
+    private ?string $instance;
 
     /**
      * http://developer.mailchimp.com/documentation/mailchimp/guides/get-started-with-mailchimp-api-3/#errors
@@ -57,8 +57,9 @@ class MailchimpException extends \Exception
      * @param array  $errors
      * @param string $instance
      * @param \Throwable $previous
+     * @todo Fix $status: Optional parameter is provided before required.
      */
-    public function __construct($status=0, $detail, $type, $title, $errors=null, $instance=null, \Throwable $previous=null)
+    public function __construct($status = 0, $detail, $type, $title, $errors = null, $instance = null, \Throwable $previous=null)
     {
         parent::__construct($detail, $status, $previous);
 
@@ -75,7 +76,7 @@ public function __construct($status=0, $detail, $type, $title, $errors=null, $in
      *
      * @return static
      */
-    public function setType($type)
+    public function setType(string $type): static
     {
         $this->type = $type;
         return $this;
@@ -86,7 +87,7 @@ public function setType($type)
      *
      * @return static
      */
-    public function setTitle($title)
+    public function setTitle(string $title): static
     {
         $this->title = $title;
         return $this;
@@ -97,7 +98,7 @@ public function setTitle($title)
      *
      * @return static
      */
-    public function setErrors(array $errors)
+    public function setErrors(array $errors): static
     {
         $this->errors = $errors;
         return $this;
@@ -108,7 +109,7 @@ public function setErrors(array $errors)
      *
      * @return static
      */
-    public function setInstance($instance)
+    public function setInstance(string $instance): static
     {
         $this->instance = $instance;
         return $this;
@@ -117,7 +118,7 @@ public function setInstance($instance)
     /**
      * @return int
      */
-    public function getStatus()
+    public function getStatus(): int
     {
         return $this->status;
     }
@@ -125,7 +126,7 @@ public function getStatus()
     /**
      * @return string
      */
-    public function getDetail()
+    public function getDetail(): string
     {
         return $this->detail;
     }
@@ -133,7 +134,7 @@ public function getDetail()
     /**
      * @return string
      */
-    public function getType()
+    public function getType(): string
     {
         return $this->type;
     }
@@ -141,7 +142,7 @@ public function getType()
     /**
      * @return string
      */
-    public function getTitle()
+    public function getTitle(): string
     {
         return $this->title;
     }
@@ -149,13 +150,14 @@ public function getTitle()
     /**
      * @return string
      */
-    public function getInstance()
+    public function getInstance(): ?string
     {
         return $this->instance;
     }
 
     /**
      * @return
+     * @todo: Artifact?
      */
     public function getString()
     {
@@ -163,9 +165,9 @@ public function getString()
     }
 
     /**
-     * @return array
+     * @return array|null
      */
-    public function getErrors()
+    public function getErrors(): ?array
     {
         return $this->errors;
     }
diff --git a/src/Provider/ConfigListProvider.php b/src/Provider/ConfigListProvider.php
index bc39e41..9642259 100644
--- a/src/Provider/ConfigListProvider.php
+++ b/src/Provider/ConfigListProvider.php
@@ -2,13 +2,13 @@
 
 namespace Welp\MailchimpBundle\Provider;
 
-use Welp\MailchimpBundle\Provider\ListProviderInterface;
 use Welp\MailchimpBundle\Subscriber\SubscriberList;
+use Welp\MailchimpBundle\Subscriber\SubscriberListInterface;
 
 class ConfigListProvider implements ListProviderInterface
 {
-    private $providerFactory;
-    private $lists;
+    private ProviderFactory $providerFactory;
+    private array $lists;
 
     public function __construct(ProviderFactory $providerFactory, $lists)
     {
@@ -20,16 +20,18 @@ public function __construct(ProviderFactory $providerFactory, $lists)
      * Default list provider, retrieve the lists from the config file.
      * {@inheritdoc}
      */
-    public function getLists()
+    public function getLists(): array
     {
-        if (sizeof($this->lists) == 0) {
-            throw new \RuntimeException("No Mailchimp list has been defined. Check the your config.yml file based on MailchimpBundle's README.md");
+        if (count($this->lists) === 0) {
+            throw new \RuntimeException('No Mailchimp list has been defined. Check the your config.yml file based on MailchimpBundle\'s README.md');
         }
-        $lists = array();
-        foreach ($this->lists as $listId => $listParameters) 
-        {            
+
+        $lists = [];
+
+        foreach ($this->lists as $listId => $listParameters) {
             $lists[] = $this->createList($listId, $listParameters);            
         }
+
         return $lists;
     }
 
@@ -37,24 +39,24 @@ public function getLists()
      * Default list provider, retrieve one list from the config file.
      * {@inheritdoc}
      */
-    public function getList($listId)
+    public function getList($listId): SubscriberListInterface
     {
-        foreach ($this->lists as $id => $listParameters) 
-        {
-            if($id == $listId)
-            {
+        foreach ($this->lists as $id => $listParameters) {
+            if ($id === $listId) {
                 return $this->createList($id, $listParameters);
             }
         }
+
+        throw new \RuntimeException('Selected Mailchimp list has not been found. Check the your config.yml file based on MailchimpBundle\'s README.md');
     }
     
     /**
      * create one SubscriberList
      * @param string $listId
-     * @param string $listParameters
+     * @param array  $listParameters
      * @return SubscriberList 
      */
-    private function createList($listId, $listParameters)
+    private function createList(string $listId, array $listParameters): SubscriberList
     {
         $providerServiceKey = $listParameters['subscriber_provider'];
         $provider = $this->providerFactory->create($providerServiceKey);
diff --git a/src/Provider/DynamicProviderInterface.php b/src/Provider/DynamicProviderInterface.php
index 17d92a8..c5541ea 100644
--- a/src/Provider/DynamicProviderInterface.php
+++ b/src/Provider/DynamicProviderInterface.php
@@ -14,5 +14,5 @@ interface DynamicProviderInterface extends ProviderInterface
      * @param  string $listId
      * @return void
      */
-    public function setListId(string $listId);
+    public function setListId(string $listId): void;
 }
diff --git a/src/Provider/ExampleSubscriberProvider.php b/src/Provider/ExampleSubscriberProvider.php
index 1536b50..f49da3c 100644
--- a/src/Provider/ExampleSubscriberProvider.php
+++ b/src/Provider/ExampleSubscriberProvider.php
@@ -27,11 +27,11 @@ public function __construct(UserRepository $userRepository)
     /**
      * {@inheritdoc}
      */
-    public function getSubscribers()
+    public function getSubscribers(): array
     {
         $users = $this->userRepository->findSubscribers();
 
-        $subscribers = array_map(function (User $user) {
+        $subscribers = array_map(static function (User $user) {
             $subscriber = new Subscriber($user->getEmail(), [
                 self::TAG_NICKNAME => $user->getNickname(),
                 self::TAG_GENDER => $user->getGender(),
diff --git a/src/Provider/FosSubscriberProvider.php b/src/Provider/FosSubscriberProvider.php
index f041656..0a34387 100644
--- a/src/Provider/FosSubscriberProvider.php
+++ b/src/Provider/FosSubscriberProvider.php
@@ -25,13 +25,13 @@ public function __construct(UserManagerInterface $userManager)
     /**
      * {@inheritdoc}
      */
-    public function getSubscribers()
+    public function getSubscribers(): array
     {
         $users = $this->userManager->findUsers();
         // or find only enabled users :
         // $users = $this->userManager->findUserBy(array('enabled' => true));
 
-        $subscribers = array_map(function (User $user) {
+        $subscribers = array_map(static function (User $user) {
             $subscriber = new Subscriber($user->getEmail(), [
                 self::TAG_USERNAME => $user->getUsername(),
                 self::TAG_ENABLED => $user->isEnabled(),
diff --git a/src/Provider/ListProviderInterface.php b/src/Provider/ListProviderInterface.php
index c80825d..98f8192 100644
--- a/src/Provider/ListProviderInterface.php
+++ b/src/Provider/ListProviderInterface.php
@@ -2,6 +2,8 @@
 
 namespace Welp\MailchimpBundle\Provider;
 
+use Welp\MailchimpBundle\Subscriber\SubscriberListInterface;
+
 /**
  * List provider interface
  */
@@ -11,11 +13,12 @@ interface ListProviderInterface
      * Get all the available Mailchimp lists
      * @return array of SubscriberListInterface
      */
-    public function getLists();
+    public function getLists(): array;
 
     /**
      * Get one Mailchimp list by id
+     * @param $listId
      * @return SubscriberListInterface
      */
-    public function getList($listId);
+    public function getList($listId): SubscriberListInterface;
 }
diff --git a/src/Provider/ProviderFactory.php b/src/Provider/ProviderFactory.php
index 65ace96..ccc730d 100644
--- a/src/Provider/ProviderFactory.php
+++ b/src/Provider/ProviderFactory.php
@@ -9,7 +9,7 @@ class ProviderFactory
      *
      * @var array
      */
-    private $providers;
+    private array $providers;
 
     /**
      * Add a provider to the provider array.
@@ -28,7 +28,7 @@ public function addProvider(string $providerKey, ProviderInterface $provider): v
      *
      * @return ProviderInterface $provider
      */
-    public function create($providerKey)
+    public function create(string $providerKey): ProviderInterface
     {
         if (!isset($this->providers[$providerKey])) {
             throw new \InvalidArgumentException(sprintf('Provider "%s" should be defined as a service.', $providerKey));
diff --git a/src/Provider/ProviderInterface.php b/src/Provider/ProviderInterface.php
index 1aee611..92a4a62 100644
--- a/src/Provider/ProviderInterface.php
+++ b/src/Provider/ProviderInterface.php
@@ -12,5 +12,5 @@ interface ProviderInterface
      * in order to sync with MailChimp List
      * @return array of Subscriber
      */
-    public function getSubscribers();
+    public function getSubscribers(): array;
 }
diff --git a/src/Resources/config/routing.yml b/src/Resources/config/routing.yml
deleted file mode 100644
index c4033b7..0000000
--- a/src/Resources/config/routing.yml
+++ /dev/null
@@ -1,3 +0,0 @@
-welp_mailchimp_webhook:
-    resource: Welp\MailchimpBundle\Controller\WebhookController
-    type:     annotation
diff --git a/src/Subscriber/ListRepository.php b/src/Subscriber/ListRepository.php
index b43666d..6a03859 100644
--- a/src/Subscriber/ListRepository.php
+++ b/src/Subscriber/ListRepository.php
@@ -3,7 +3,6 @@
 namespace Welp\MailchimpBundle\Subscriber;
 
 use DrewM\MailChimp\MailChimp;
-use phpDocumentor\Reflection\Types\Void_;
 use Welp\MailchimpBundle\Exception\MailchimpException;
 
 /**
@@ -15,19 +14,19 @@ class ListRepository
      * Numbers of subscribers per batch
      * @var int
      */
-    const SUBSCRIBER_BATCH_SIZE = 300;
+    public const SUBSCRIBER_BATCH_SIZE = 300;
 
     /**
      * MailChimp count limit for result set
      * @var int
      */
-    const MAILCHIMP_DEFAULT_COUNT_LIMIT = 10;
+    public const MAILCHIMP_DEFAULT_COUNT_LIMIT = 10;
 
     /**
      * MailChimp Object
      * @var MailChimp
      */
-    protected $mailchimp;
+    protected MailChimp $mailchimp;
 
     /**
      * @param MailChimp $mailchimp
@@ -41,23 +40,25 @@ public function __construct(MailChimp $mailchimp)
      * Get MailChimp Object to do custom actions
      * @return MailChimp https://github.com/drewm/mailchimp-api
      */
-    public function getMailChimp()
+    public function getMailChimp(): MailChimp
     {
         return $this->mailchimp;
     }
 
     /**
-     * Find MailChimp List by list Id
+     * Find MailChimp List by list ID
      * @param string $listId
-     * @return array list http://developer.mailchimp.com/documentation/mailchimp/reference/lists/#read-get_lists_list_id
+     * @return array list https://mailchimp.com/developer/marketing/api/lists/get-list-info/
+     * @throws MailchimpException
      */
-    public function findById($listId)
+    public function findById(string $listId): array
     {
-        $listData = $this->mailchimp->get("lists/$listId");
+        $listData = $this->mailchimp->get('lists/' . $listId);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
         }
+
         return $listData;
     }
 
@@ -67,14 +68,17 @@ public function findById($listId)
      * @param Subscriber $subscriber
      * @param string $status
      * @return array
+     * @throws MailchimpException
      */
-    protected function putSubscriberInList($listId, Subscriber $subscriber, $status)
+    protected function putSubscriberInList(string $listId, Subscriber $subscriber, string $status): array
     {
         if (!in_array($status, ['subscribed', 'unsubscribed', 'cleaned', 'pending', 'transactional'])) {
             throw new \RuntimeException('$status must be one of these values: subscribed, unsubscribed, cleaned, pending, transactional');
         }
+
         $subscriberHash = MailChimp::subscriberHash($subscriber->getEmail());
-        $result = $this->mailchimp->put("lists/$listId/members/$subscriberHash",
+
+        $result = $this->mailchimp->put('lists/' . $listId . '/members/' . $subscriberHash,
             array_merge(
                 $subscriber->formatMailChimp(),
                 ['status' => $status]
@@ -93,8 +97,9 @@ protected function putSubscriberInList($listId, Subscriber $subscriber, $status)
      * @param string $listId
      * @param Subscriber $subscriber
      * @return array
+     * @throws MailchimpException
      */
-    public function subscribe($listId, Subscriber $subscriber)
+    public function subscribe(string $listId, Subscriber $subscriber): array
     {
         return $this->putSubscriberInList($listId, $subscriber, 'subscribed');
     }
@@ -103,8 +108,9 @@ public function subscribe($listId, Subscriber $subscriber)
      * Subscribe a Subscriber to a list
      * @param string $listId
      * @param Subscriber $subscriber
+     * @throws MailchimpException
      */
-    public function unsubscribe($listId, Subscriber $subscriber)
+    public function unsubscribe(string $listId, Subscriber $subscriber): array
     {
         return $this->putSubscriberInList($listId, $subscriber, 'unsubscribed');
     }
@@ -113,8 +119,10 @@ public function unsubscribe($listId, Subscriber $subscriber)
      * Clean a Subscriber to a list
      * @param string $listId
      * @param Subscriber $subscriber
+     * @return array
+     * @throws MailchimpException
      */
-    public function clean($listId, Subscriber $subscriber)
+    public function clean(string $listId, Subscriber $subscriber): array
     {
         return $this->putSubscriberInList($listId, $subscriber, 'cleaned');
     }
@@ -123,8 +131,10 @@ public function clean($listId, Subscriber $subscriber)
      * Add/set pending a Subscriber to a list
      * @param string $listId
      * @param Subscriber $subscriber
+     * @return array
+     * @throws MailchimpException
      */
-    public function pending($listId, Subscriber $subscriber)
+    public function pending(string $listId, Subscriber $subscriber): array
     {
         return $this->putSubscriberInList($listId, $subscriber, 'pending');
     }
@@ -133,22 +143,26 @@ public function pending($listId, Subscriber $subscriber)
      * set transactional a Subscriber to a list
      * @param string $listId
      * @param Subscriber $subscriber
+     * @return array
+     * @throws MailchimpException
      */
-    public function transactional($listId, Subscriber $subscriber)
+    public function transactional(string $listId, Subscriber $subscriber): array
     {
         return $this->putSubscriberInList($listId, $subscriber, 'transactional');
     }
 
     /**
      * Update a Subscriber to a list
-     * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/members/#edit-patch_lists_list_id_members_subscriber_hash
+     * https://mailchimp.com/developer/marketing/api/list-members/update-list-member/
      * @param string $listId
      * @param Subscriber $subscriber
+     * @return array|bool
+     * @throws MailchimpException
      */
-    public function update($listId, Subscriber $subscriber)
+    public function update(string $listId, Subscriber $subscriber): bool|array
     {
         $subscriberHash = MailChimp::subscriberHash($subscriber->getEmail());
-        $result = $this->mailchimp->patch("lists/$listId/members/$subscriberHash", $subscriber->formatMailChimp());
+        $result = $this->mailchimp->patch('lists/' . $listId . '/members/' . $subscriberHash, $subscriber->formatMailChimp());
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -162,20 +176,23 @@ public function update($listId, Subscriber $subscriber)
      *       one possible solution is to delete old subscriber and add a new one
      *       with the same mergeFieds and Options...
      * Change email address
-     * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/members/#edit-put_lists_list_id_members_subscriber_hash
+     * https://mailchimp.com/developer/marketing/api/list-members/update-list-member/
      * @param string $listId
      * @param Subscriber $newSubscriber
      * @param string $oldEmailAddress
+     * @return array|bool
+     * @throws MailchimpException
      */
-    public function changeEmailAddress($listId, Subscriber $newSubscriber, $oldEmailAddress)
+    public function changeEmailAddress(string $listId, Subscriber $newSubscriber, string $oldEmailAddress): bool|array
     {
         # @NOTE handle special cases:
         #       1. new email address already exists in List
         #       2. old email address not exists in list
-        #       3. old or new email address doesn't exists in list
+        #       3. old or new email address doesn't exist in list
 
         $subscriberHash = MailChimp::subscriberHash($oldEmailAddress);
-        $oldMember = $this->mailchimp->get("lists/$listId/members/$subscriberHash");
+        $oldMember = $this->mailchimp->get('lists/' . $listId . '/members/' . $subscriberHash);
+
         if (!$this->mailchimp->success()) {
             // problem with the oldSubcriber (doest not exist, ...)
             // np we will take the new Subscriber
@@ -183,21 +200,15 @@ public function changeEmailAddress($listId, Subscriber $newSubscriber, $oldEmail
             $newMember['status_if_new'] = 'subscribed';
         } else {
             // clean member
-            unset($oldMember['_links']);
-            unset($oldMember['id']);
-            unset($oldMember['stats']);
-            unset($oldMember['unique_email_id']);
-            unset($oldMember['member_rating']);
-            unset($oldMember['last_changed']);
-            unset($oldMember['email_client']);
-            unset($oldMember['list_id']);
+            unset($oldMember['_links'], $oldMember['id'], $oldMember['stats'], $oldMember['unique_email_id'], $oldMember['member_rating'], $oldMember['last_changed'], $oldMember['email_client'], $oldMember['list_id']);
 
             $newMember = $oldMember;
             $newMember['email_address'] = $newSubscriber->getEmail();
             $newMember['status_if_new'] = 'subscribed';
 
             // delete the old Member
-            $deleteOld = $this->mailchimp->delete("lists/$listId/members/$subscriberHash");
+            $deleteOld = $this->mailchimp->delete('lists/' . $listId . '/members/' . $subscriberHash);
+
             if (!$this->mailchimp->success()) {
                 $this->throwMailchimpError($this->mailchimp->getLastResponse());
             }
@@ -205,7 +216,8 @@ public function changeEmailAddress($listId, Subscriber $newSubscriber, $oldEmail
 
         // add/update the new member
         $subscriberHash = MailChimp::subscriberHash($newSubscriber->getEmail());
-        $result = $this->mailchimp->put("lists/$listId/members/$subscriberHash", $newMember);
+        $result = $this->mailchimp->put('lists/' . $listId . '/members/' . $subscriberHash, $newMember);
+
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
         }
@@ -217,11 +229,13 @@ public function changeEmailAddress($listId, Subscriber $newSubscriber, $oldEmail
      * Delete a Subscriber to a list
      * @param string $listId
      * @param Subscriber $subscriber
+     * @return array|bool
+     * @throws MailchimpException
      */
-    public function delete($listId, Subscriber $subscriber)
+    public function delete(string $listId, Subscriber $subscriber): bool|array
     {
         $subscriberHash = MailChimp::subscriberHash($subscriber->getEmail());
-        $result = $this->mailchimp->delete("lists/$listId/members/$subscriberHash");
+        $result = $this->mailchimp->delete('lists/' . $listId . '/members/' . $subscriberHash);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -236,24 +250,32 @@ public function delete($listId, Subscriber $subscriber)
      * @param array $subscribers
      * @return array $batchIds
      */
-    public function batchSubscribe($listId, array $subscribers)
+    public function batchSubscribe(string $listId, array $subscribers): array
     {
         $batchResults = [];
         // as suggested in MailChimp API docs, we send multiple smaller requests instead of a bigger one
         $subscriberChunks = array_chunk($subscribers, self::SUBSCRIBER_BATCH_SIZE);
+
         foreach ($subscriberChunks as $subscriberChunk) {
-            $Batch = $this->mailchimp->new_batch();
+            $batch = $this->mailchimp->new_batch();
+
             foreach ($subscriberChunk as $index => $newsubscribers) {
                 $subscriberHash = MailChimp::subscriberHash($newsubscribers->getEmail());
-                $Batch->put("op$index", "lists/$listId/members/$subscriberHash", array_merge(
-                    $newsubscribers->formatMailChimp(),
-                    ['status' => 'subscribed']
-                ));
+
+                $batch->put(
+                    'op' . $index,
+                    'lists/' . $listId . '/members/' . $subscriberHash,
+                    array_merge(
+                        $newsubscribers->formatMailChimp(),
+                        ['status' => 'subscribed']
+                    )
+                );
             }
-            $Batch->execute();
-            $currentBatch = $Batch->check_status();
-            array_push($batchResults, $currentBatch);
+            $batch->execute();
+            $currentBatch = $batch->check_status();
+            $batchResults[] = $currentBatch; // faster than array_push() here
         }
+
         return $batchResults;
     }
 
@@ -263,23 +285,28 @@ public function batchSubscribe($listId, array $subscribers)
      * @param array $emails
      * @return array $batchIds
      */
-    public function batchUnsubscribe($listId, array $emails)
+    public function batchUnsubscribe(string $listId, array $emails): array
     {
         $batchIds = [];
         // as suggested in MailChimp API docs, we send multiple smaller requests instead of a bigger one
         $emailsChunks = array_chunk($emails, self::SUBSCRIBER_BATCH_SIZE);
+
         foreach ($emailsChunks as $emailsChunk) {
-            $Batch = $this->mailchimp->new_batch();
+            $batch = $this->mailchimp->new_batch();
+
             foreach ($emailsChunk as $index => $email) {
                 $emailHash = MailChimp::subscriberHash($email);
-                $Batch->patch("op$index", "lists/$listId/members/$emailHash", [
+                $batch->patch('op' . $index, 'lists/' . $listId . '/members/' . $emailHash, [
                     'status' => 'unsubscribed'
                 ]);
             }
-            $result = $Batch->execute();
-            $currentBatch = $Batch->check_status();
-            array_push($batchIds, $currentBatch['id']);
+
+            $batch->execute();
+            $currentBatch = $batch->check_status();
+
+            $batchIds[] = $currentBatch['id']; // faster than array_push() here
         }
+
         return $batchIds;
     }
 
@@ -289,20 +316,23 @@ public function batchUnsubscribe($listId, array $emails)
      * @param array $emails
      * @return array $batchIds
      */
-    public function batchDelete($listId, array $emails)
+    public function batchDelete(string $listId, array $emails): array
     {
         $batchIds = [];
         // as suggested in MailChimp API docs, we send multiple smaller requests instead of a bigger one
         $emailsChunks = array_chunk($emails, self::SUBSCRIBER_BATCH_SIZE);
+
         foreach ($emailsChunks as $emailsChunk) {
-            $Batch = $this->mailchimp->new_batch();
+            $batch = $this->mailchimp->new_batch();
+
             foreach ($emailsChunk as $index => $email) {
                 $emailHash = MailChimp::subscriberHash($email);
-                $Batch->delete("op$index", "lists/$listId/members/$emailHash");
+                $batch->delete('op' . $index, 'lists/' . $listId . '/members/' . $emailHash);
             }
-            $result = $Batch->execute();
-            $currentBatch = $Batch->check_status();
-            array_push($batchIds, $currentBatch['id']);
+
+            $batch->execute();
+            $currentBatch = $batch->check_status();
+            $batchIds[] = $currentBatch['id'];
         }
         return $batchIds;
     }
@@ -311,11 +341,11 @@ public function batchDelete($listId, array $emails)
      * Get Members of a list
      * @param string $listId
      * @return array
+     * @throws MailchimpException
      */
-    public function getMembers($listId)
+    public function getMembers(string $listId): array
     {
-        $emails = [];
-        $result = $this->mailchimp->get("lists/$listId/members");
+        $result = $this->mailchimp->get('lists/' . $listId . '/members');
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -328,14 +358,15 @@ public function getMembers($listId)
      * Get an array of subscribers emails from a list
      * @param string $listId
      * @return array
+     * @throws MailchimpException
      */
-    public function getSubscriberEmails($listId)
+    public function getSubscriberEmails(string $listId): array
     {
         $emails = [];
         $members = [];
-        $offset=0;
+        $offset = 0;
         $maxresult = 200;
-        $result = $this->mailchimp->get("lists/$listId/members", ['count'=> $maxresult]);
+        $result = $this->mailchimp->get('lists/' . $listId . '/members', ['count' => $maxresult]);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -345,20 +376,21 @@ public function getSubscriberEmails($listId)
         $members = array_merge($members, $result['members']);
 
         while ($offset < $totalItems) {
-            $offset+=$maxresult;
-            $result = $this->mailchimp->get("lists/$listId/members", [
-                        'count'         => $maxresult,
-                        'offset'        => $offset
-                    ]);
+            $offset += $maxresult;
+            $result = $this->mailchimp->get('lists/' . $listId . '/members', [
+                'count' => $maxresult,
+                'offset' => $offset
+            ]);
 
             if (!$this->mailchimp->success()) {
                 $this->throwMailchimpError($this->mailchimp->getLastResponse());
             }
+
             $members = array_merge($members, $result['members']);
-        };
+        }
 
         foreach ($members as $key => $member) {
-            array_push($emails, $member['email_address']);
+            $emails[] = $member['email_address'];
         }
 
         return $emails;
@@ -366,17 +398,18 @@ public function getSubscriberEmails($listId)
 
     /**
      * find all merge fields for a list
-     * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/merge-fields/#
+     * https://mailchimp.com/developer/marketing/api/list-merges/
      * @param string $listId
      * @return array
+     * @throws MailchimpException
      */
-    public function getMergeFields($listId)
+    public function getMergeFields(string $listId): array
     {
-        $result = $this->mailchimp->get("lists/$listId/merge-fields");
+        $result = $this->mailchimp->get('lists/' . $listId . '/merge-fields');
 
         # Handle mailchimp default count limit
         if ($result['total_items'] > self::MAILCHIMP_DEFAULT_COUNT_LIMIT) {
-            $result = $this->mailchimp->get("lists/$listId/merge-fields", array("count" => $result['total_items']));
+            $result = $this->mailchimp->get('lists/' . $listId . '/merge-fields', ['count' => $result['total_items']]);
         }
 
         if (!$this->mailchimp->success()) {
@@ -388,14 +421,15 @@ public function getMergeFields($listId)
 
     /**
      * add merge field for a list
-     * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/merge-fields/#
+     * https://mailchimp.com/developer/marketing/api/list-merges/
      * @param string $listId
      * @param array $mergeData ["name" => '', "type" => '']
      * @return array
+     * @throws MailchimpException
      */
-    public function addMergeField($listId, array $mergeData)
+    public function addMergeField(string $listId, array $mergeData): array
     {
-        $result = $this->mailchimp->post("lists/$listId/merge-fields", $mergeData);
+        $result = $this->mailchimp->post('lists/' . $listId . '/merge-fields', $mergeData);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -406,15 +440,16 @@ public function addMergeField($listId, array $mergeData)
 
     /**
      * add merge field for a list
-     * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/merge-fields/#edit-patch_lists_list_id_merge_fields_merge_id
+     * https://mailchimp.com/developer/marketing/api/list-merges/
      * @param string $listId
      * @param string $mergeId
      * @param array $mergeData ["name" => '', "type" => '', ...]
      * @return array
+     * @throws MailchimpException
      */
-    public function updateMergeField($listId, $mergeId, $mergeData)
+    public function updateMergeField(string $listId, string $mergeId, array $mergeData): array
     {
-        $result = $this->mailchimp->patch("lists/$listId/merge-fields/$mergeId", $mergeData);
+        $result = $this->mailchimp->patch('lists/' . $listId . '/merge-fields/' . $mergeId, $mergeData);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -424,15 +459,16 @@ public function updateMergeField($listId, $mergeId, $mergeData)
     }
 
     /**
-    * delete merge field for a list
-    * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/merge-fields/#
-    * @param string $listId
-    * @param string $mergeId
-    * @return array
-    */
-    public function deleteMergeField($listId, $mergeId)
+     * delete merge field for a list
+     * https://mailchimp.com/developer/marketing/api/list-merges/
+     * @param string $listId
+     * @param string $mergeId
+     * @return array
+     * @throws MailchimpException
+     */
+    public function deleteMergeField(string $listId, string $mergeId): array
     {
-        $result = $this->mailchimp->delete("lists/$listId/merge-fields/$mergeId");
+        $result = $this->mailchimp->delete('lists/' . $listId . '/merge-fields/' . $mergeId);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -442,12 +478,13 @@ public function deleteMergeField($listId, $mergeId)
     }
 
     /**
-    * Automatically configure Webhook for a list
-    * @param string $listId
-    * @param string $webhookurl
-    * @return array
-    */
-    public function registerMainWebhook($listId, $webhookurl)
+     * Automatically configure Webhook for a list
+     * @param string $listId
+     * @param string $webhookurl
+     * @return array
+     * @throws MailchimpException
+     */
+    public function registerMainWebhook(string $listId, string $webhookurl): array
     {
         // Configure webhook
         $subscribeWebhook = [
@@ -463,7 +500,7 @@ public function registerMainWebhook($listId, $webhookurl)
             'sources' => [
                 'user'  => true,
                 'admin' => true,
-                'api'   => false // to avoid double (infinite loop) update (update an subscriber with the API and the webhook reupdate the user, ...)
+                'api'   => false // to avoid double (infinite loop) update (update a subscriber with the API and the webhook reupdate the user, ...)
             ]
         ];
 
@@ -471,15 +508,16 @@ public function registerMainWebhook($listId, $webhookurl)
     }
 
     /**
-    * Add a new webhook to a list
-    * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/webhooks/#
-    * @param string $listId
-    * @param array $webhookData
-    * @return array
-    */
-    public function addWebhook($listId, array $webhookData)
+     * Add a new webhook to a list
+     * https://mailchimp.com/developer/marketing/api/list-webhooks/
+     * @param string $listId
+     * @param array $webhookData
+     * @return array
+     * @throws MailchimpException
+     */
+    public function addWebhook(string $listId, array $webhookData): array
     {
-        $result = $this->mailchimp->post("lists/$listId/webhooks", $webhookData);
+        $result = $this->mailchimp->post('lists/' . $listId . '/webhooks', $webhookData);
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -489,14 +527,15 @@ public function addWebhook($listId, array $webhookData)
     }
 
     /**
-    * Get webhooks of a list
-    * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/webhooks/#
-    * @param string $listId
-    * @return array
-    */
-    public function getWebhooks($listId)
+     * Get webhooks of a list
+     * https://mailchimp.com/developer/marketing/api/list-webhooks/
+     * @param string $listId
+     * @return array
+     * @throws MailchimpException
+     */
+    public function getWebhooks(string $listId): array
     {
-        $result = $this->mailchimp->get("lists/$listId/webhooks");
+        $result = $this->mailchimp->get('lists/' . $listId . '/webhooks');
 
         if (!$this->mailchimp->success()) {
             $this->throwMailchimpError($this->mailchimp->getLastResponse());
@@ -507,31 +546,41 @@ public function getWebhooks($listId)
 
     /**
      * [throwMailchimpError description]
-     * @param  array  $errorResponse [description]
+     * @param array $errorResponse [description]
      * @return void
      * @throws MailchimpException [description]
      */
-    private function throwMailchimpError(array $errorResponse)
+    private function throwMailchimpError(array $errorResponse): void
     {
-        $errorArray = json_decode($errorResponse['body'], true);
-        if (is_array($errorArray) && array_key_exists('errors', $errorArray)) {
+        try {
+            $errorArray = json_decode($errorResponse['body'], true, 512, JSON_THROW_ON_ERROR);
+        } catch (\JsonException $e) {
             throw new MailchimpException(
-                $errorArray['status'],
-                $errorArray['detail'],
-                $errorArray['type'],
-                $errorArray['title'],
-                $errorArray['errors'],
-                $errorArray['instance']
+                400,
+                $e->getMessage(),
+                'JSON',
+                'Invalid JSON response.',
             );
-        } else {
+        }
+
+        if (is_array($errorArray) && array_key_exists('errors', $errorArray)) {
             throw new MailchimpException(
                 $errorArray['status'],
                 $errorArray['detail'],
                 $errorArray['type'],
                 $errorArray['title'],
-                null,
+                $errorArray['errors'],
                 $errorArray['instance']
             );
         }
+
+        throw new MailchimpException(
+            $errorArray['status'],
+            $errorArray['detail'],
+            $errorArray['type'],
+            $errorArray['title'],
+            null,
+            $errorArray['instance']
+        );
     }
 }
diff --git a/src/Subscriber/ListSynchronizer.php b/src/Subscriber/ListSynchronizer.php
index 55c6a23..e21cf65 100644
--- a/src/Subscriber/ListSynchronizer.php
+++ b/src/Subscriber/ListSynchronizer.php
@@ -2,6 +2,8 @@
 
 namespace Welp\MailchimpBundle\Subscriber;
 
+use Welp\MailchimpBundle\Exception\MailchimpException;
+
 /**
  * Handle Synchronization between SubscriberList and specific MailChimp List
  */
@@ -10,7 +12,7 @@ class ListSynchronizer
     /**
      * @var ListRepository
      */
-    protected $listRepository;
+    protected ListRepository $listRepository;
 
     /**
      * @param ListRepository $listRepository
@@ -23,9 +25,10 @@ public function __construct(ListRepository $listRepository)
     /**
      * Synchronise user from provider with MailChimp List
      * @param SubscriberListInterface $list
-     * @return void
+     * @return array
+     * @throws MailchimpException
      */
-    public function synchronize(SubscriberListInterface $list)
+    public function synchronize(SubscriberListInterface $list): array
     {
         $listData = $this->listRepository->findById($list->getListId());
 
@@ -34,6 +37,7 @@ public function synchronize(SubscriberListInterface $list)
 
         // unsubscribe difference
         $this->unsubscribeDifference($list->getListId(), $subscribers);
+
         // subscribe the rest
         return $this->batchSubscribe($list->getListId(), $subscribers);
     }
@@ -42,29 +46,31 @@ public function synchronize(SubscriberListInterface $list)
      * Subscribe a batch of user
      * @param string $listId
      * @param array $subscribers
-     * @return void
+     * @return array
      */
-    protected function batchSubscribe($listId, array $subscribers = [])
+    protected function batchSubscribe(string $listId, array $subscribers = []): array
     {
         return $this->listRepository->batchSubscribe($listId, $subscribers);
     }
 
     /**
-     * Unsubscribe the difference between the array subscriber an user
+     * Unsubscribe the difference between the array subscriber a user
      * @param string $listId
      * @param array $subscribers
      * @return void
+     * @throws MailchimpException
      */
-    protected function unsubscribeDifference($listId, array $subscribers)
+    protected function unsubscribeDifference(string $listId, array $subscribers): void
     {
         $mailchimpEmails = $this->listRepository->getSubscriberEmails($listId);
-        $internalEmails = array_map(function (Subscriber $subscriber) {
+        $internalEmails = array_map(static function (Subscriber $subscriber) {
             return $subscriber->getEmail();
         }, $subscribers);
 
         // emails that are present in mailchimp but not internally should be unsubscribed
         $diffenceEmails = array_diff($mailchimpEmails, $internalEmails);
-        if (sizeof($diffenceEmails) == 0) {
+
+        if (count($diffenceEmails) === 0) {
             return;
         }
 
@@ -76,8 +82,9 @@ protected function unsubscribeDifference($listId, array $subscribers)
      * @param string $listId
      * @param array $mergeFields
      * @return void
+     * @throws MailchimpException
      */
-    public function synchronizeMergeFields($listId, array $mergeFields = [])
+    public function synchronizeMergeFields(string $listId, array $mergeFields = []): void
     {
         $mailChimpMergeFields = $this->listRepository->getMergeFields($listId);
 
@@ -99,21 +106,23 @@ public function synchronizeMergeFields($listId, array $mergeFields = [])
     }
 
     /**
-    * Test if the merge field Tag exists in an array
-    * @param string $tagName
-    * @param array $tags
-    * @return mixed (Boolean true|false) or $tag['merge_id']
-    */
-    protected function tagExists($tagName, array $tags)
+     * Test if the merge field Tag exists in an array
+     * @param string $tagName
+     * @param array $tags
+     * @return bool|string (Boolean true|false) or $tag['merge_id']
+     */
+    protected function tagExists(string $tagName, array $tags): bool|string
     {
         foreach ($tags as $tag) {
-            if ($tag['tag'] == $tagName) {
+            if ($tag['tag'] === $tagName) {
                 if (array_key_exists('merge_id', $tag)) {
                     return $tag['merge_id'];
                 }
+
                 return true;
             }
         }
+
         return false;
     }
 }
diff --git a/src/Subscriber/Subscriber.php b/src/Subscriber/Subscriber.php
index 93a96bc..a4d7fc2 100644
--- a/src/Subscriber/Subscriber.php
+++ b/src/Subscriber/Subscriber.php
@@ -4,7 +4,7 @@
 
 /**
  * Class to represent a subscriber
- * http://developer.mailchimp.com/documentation/mailchimp/reference/lists/members/
+ * https://mailchimp.com/developer/marketing/api/list-members/
  */
 class Subscriber
 {
@@ -12,19 +12,19 @@ class Subscriber
      * Subscriber's email
      * @var string
      */
-    protected $email;
+    protected string $email;
 
     /**
      * Subscriber's merge fields
      * @var array
      */
-    protected $mergeFields;
+    protected array $mergeFields;
 
     /**
      * Subscriber's options
      * @var array
      */
-    protected $options;
+    protected array $options;
 
     /**
      *
@@ -32,7 +32,7 @@ class Subscriber
      * @param array $mergeFields
      * @param array $options
      */
-    public function __construct($email, array $mergeFields = [], array $options = [])
+    public function __construct(string $email, array $mergeFields = [], array $options = [])
     {
         $this->email = $email;
         $this->mergeFields = $mergeFields;
@@ -40,10 +40,10 @@ public function __construct($email, array $mergeFields = [], array $options = []
     }
 
     /**
-     * Formate Subscriber for MailChimp API request
+     * Format Subscriber for MailChimp API request
      * @return array
      */
-    public function formatMailChimp()
+    public function formatMailChimp(): array
     {
         $options = $this->options;
         if (!empty($this->getMergeFields())) {
@@ -61,7 +61,7 @@ public function formatMailChimp()
      * Correspond to email_address in MailChimp request
      * @return string
      */
-    public function getEmail()
+    public function getEmail(): string
     {
         return $this->email;
     }
@@ -71,9 +71,9 @@ public function getEmail()
      * @param array $mergeFields
      * @return array ['TAGKEY' => value, ...]
      */
-    public function setMergeFields(array $mergeFields)
+    public function setMergeFields(array $mergeFields): array
     {
-        // since fev2017, MailChimp API doesn't handle null value en throw 400
+        // since feb2017, MailChimp API doesn't handle null value en throw 400
         // errors when you try to add subscriber with a mergefields value to null
         foreach ($mergeFields as $key => $value) {
             if ($value === null) {
@@ -89,7 +89,7 @@ public function setMergeFields(array $mergeFields)
      * Correspond to merge_fields in MailChimp request
      * @return array ['TAGKEY' => value, ...]
      */
-    public function getMergeFields()
+    public function getMergeFields(): array
     {
         // since fev2017, MailChimp API doesn't handle null value en throw 400
         // errors when you try to add subscriber with a mergefields value to null
@@ -98,6 +98,7 @@ public function getMergeFields()
                 unset($this->mergeFields[$key]);
             }
         }
+
         return $this->mergeFields;
     }
 
@@ -106,7 +107,7 @@ public function getMergeFields()
      * email_type, interests, language, vip, location, ip_signup, timestamp_signup, ip_opt, timestamp_opt
      * @return array
      */
-    public function getOptions()
+    public function getOptions(): array
     {
         return $this->options;
     }
diff --git a/src/Subscriber/SubscriberList.php b/src/Subscriber/SubscriberList.php
index 8aca8b5..9376478 100644
--- a/src/Subscriber/SubscriberList.php
+++ b/src/Subscriber/SubscriberList.php
@@ -14,39 +14,39 @@ class SubscriberList implements SubscriberListInterface
      * MailChimp ListId
      * @var string
      */
-    protected $listId;
+    protected string $listId;
 
     /**
      * Subscriber provider
      * @var ProviderInterface
      */
-    protected $provider;
+    protected ProviderInterface $provider;
 
     /**
      * Merge fields
      * @var array
      */
-    protected $mergeFields;
+    protected array $mergeFields;
 
     /**
      * MailChimp webhook URL
      * @var string
      */
-    protected $webhookUrl;
-    
+    protected string $webhookUrl = '';
+
     /**
      * MailChimp webhook secret
      * @var string
      */
-    protected $webhookSecret;
+    protected string $webhookSecret = '';
 
     /**
      *
-     * @param string            $listId
+     * @param string $listId
      * @param ProviderInterface $provider
      * @param array             $mergeFields
      */
-    public function __construct($listId, ProviderInterface $provider, array $mergeFields = array())
+    public function __construct(string $listId, ProviderInterface $provider, array $mergeFields = [])
     {
         $this->listId = $listId;
         $this->provider = $provider;
@@ -55,14 +55,14 @@ public function __construct($listId, ProviderInterface $provider, array $mergeFi
         //If the provider implements DynamicProviderInterface, set the list id in the provider
         if ($this->provider instanceof DynamicProviderInterface) {
             $this->provider->setListId($this->listId);
-        }        
+        }
     }
 
     /**
      * get the MailChimp ListId
      * @return string
      */
-    public function getListId()
+    public function getListId(): string
     {
         return $this->listId;
     }
@@ -71,7 +71,7 @@ public function getListId()
      * Get the subscriber provider
      * @return ProviderInterface
      */
-    public function getProvider()
+    public function getProvider(): ProviderInterface
     {
         return $this->provider;
     }
@@ -80,7 +80,7 @@ public function getProvider()
      * Get the list merge fields
      * @return array
      */
-    public function getMergeFields()
+    public function getMergeFields(): array
     {
         return $this->mergeFields;
     }
@@ -89,16 +89,16 @@ public function getMergeFields()
      * Get the list webhook URL
      * @return string
      */
-    public function getWebhookUrl()
+    public function getWebhookUrl(): string
     {
         return $this->webhookUrl;
     }
 
     /**
      * Set the list webhook URL
-     * @param string
+     * @param string $webhookUrl
      */
-    public function setWebhookUrl($webhookUrl)
+    public function setWebhookUrl(string $webhookUrl): void
     {
         $this->webhookUrl = $webhookUrl;
     }
@@ -107,16 +107,16 @@ public function setWebhookUrl($webhookUrl)
      * Get the list webhook secret
      * @return string
      */
-    public function getWebhookSecret()
+    public function getWebhookSecret(): string
     {
         return $this->webhookSecret;
     }
 
     /**
      * Set the list webhook secret
-     * @param string
+     * @param string $webhookSecret
      */
-    public function setWebhookSecret($webhookSecret)
+    public function setWebhookSecret(string $webhookSecret): void
     {
         $this->webhookSecret = $webhookSecret;
     }
diff --git a/src/Subscriber/SubscriberListInterface.php b/src/Subscriber/SubscriberListInterface.php
index 001a60b..a6683f3 100644
--- a/src/Subscriber/SubscriberListInterface.php
+++ b/src/Subscriber/SubscriberListInterface.php
@@ -2,6 +2,8 @@
 
 namespace Welp\MailchimpBundle\Subscriber;
 
+use Welp\MailchimpBundle\Provider\ProviderInterface;
+
 /**
  * SubscriberList interface linked a MailChimpList with a SubscriberProvider
  */
@@ -11,41 +13,41 @@ interface SubscriberListInterface
      * get the MailChimp ListId
      * @return string
      */
-    public function getListId();
+    public function getListId(): string;
 
     /**
      * Get the subscriber provider
      * @return ProviderInterface
      */
-    public function getProvider();
+    public function getProvider(): ProviderInterface;
 
     /**
      * Get the list merge fields
      * @return array
      */
-    public function getMergeFields();
+    public function getMergeFields(): array;
 
     /**
      * Get the list webhook URL
      * @return string
      */
-    public function getWebhookUrl();
+    public function getWebhookUrl(): string;
 
     /**
      * Set the list webhook URL
-     * @param string
+     * @param string $webhookUrl
      */
-    public function setWebhookUrl($webhookUrl);
+    public function setWebhookUrl(string $webhookUrl);
 
     /**
      * Get the list webhook secret
      * @return string
      */
-    public function getWebhookSecret();
+    public function getWebhookSecret(): string;
 
     /**
      * Set the list webhook secret
-     * @param string
+     * @param string $webhookSecret
      */
-    public function setWebhookSecret($webhookSecret);
+    public function setWebhookSecret(string $webhookSecret);
 }
diff --git a/src/WelpMailchimpBundle.php b/src/WelpMailchimpBundle.php
index a1136e1..bd0a1f3 100644
--- a/src/WelpMailchimpBundle.php
+++ b/src/WelpMailchimpBundle.php
@@ -1,13 +1,21 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Welp\MailchimpBundle;
 
-use Symfony\Component\HttpKernel\Bundle\Bundle;
+use Symfony\Component\DependencyInjection\Extension\ExtensionInterface;
+use Symfony\Component\HttpKernel\Bundle\AbstractBundle;
 use Welp\MailchimpBundle\DependencyInjection\WelpMailchimpExtension;
 
-class WelpMailchimpBundle extends Bundle
+class WelpMailchimpBundle extends AbstractBundle
 {
-    public function getContainerExtension(): WelpMailchimpExtension
+    public function getPath(): string
+    {
+        return dirname(__DIR__);
+    }
+
+    public function getContainerExtension(): ?ExtensionInterface
     {
         return new WelpMailchimpExtension();
     }