diff --git a/src/Exceptions/InvalidRequestException.php b/src/Exceptions/InvalidRequestException.php
index 6b1e472..dca066f 100644
--- a/src/Exceptions/InvalidRequestException.php
+++ b/src/Exceptions/InvalidRequestException.php
@@ -6,15 +6,19 @@
 
 class InvalidRequestException extends PaymentException
 {
+    /**
+     * @param array<string,mixed>|null $details
+     */
     public function __construct(
         string $message = 'Invalid request',
         ?string $errorCode = null,
         ?string $errorType = null,
         ?string $declineCode = null,
         ?string $param = null,
+        ?array $details = null,
         int $code = 400,
         ?\Throwable $previous = null
     ) {
-        parent::__construct($message, $errorCode, $errorType, $declineCode, $param, $code, $previous);
+        parent::__construct($message, $errorCode, $errorType, $declineCode, $param, $details, $code, $previous);
     }
 }
diff --git a/src/Exceptions/PaymentException.php b/src/Exceptions/PaymentException.php
index f5d7b88..4529b21 100644
--- a/src/Exceptions/PaymentException.php
+++ b/src/Exceptions/PaymentException.php
@@ -6,12 +6,16 @@
 
 class PaymentException extends \RuntimeException
 {
+    /**
+     * @param array<string,mixed>|null $details
+     */
     public function __construct(
         string $message = '',
         public readonly ?string $errorCode = null,
         public readonly ?string $errorType = null,
         public readonly ?string $declineCode = null,
         public readonly ?string $param = null,
+        public readonly ?array $details = null,
         int $code = 0,
         ?\Throwable $previous = null
     ) {
diff --git a/src/Gateways/AbstractGateway.php b/src/Gateways/AbstractGateway.php
index 3e8860c..8a7a0a1 100644
--- a/src/Gateways/AbstractGateway.php
+++ b/src/Gateways/AbstractGateway.php
@@ -79,33 +79,93 @@ protected function sendRequest($request): array
 
     protected function handleErrorResponse(array $response, int $statusCode): void
     {
-        $error = $response['error'] ?? [];
-        $message = $error['message'] ?? 'An error occurred with the payment gateway';
-        $code = $error['code'] ?? null;
-        $type = $error['type'] ?? null;
-        $declineCode = $error['decline_code'] ?? null;
-        $param = $error['param'] ?? null;
+        $error = isset($response['error']) && is_array($response['error'])
+            ? $response['error']
+            : $response;
+
+        $message = $this->extractErrorMessage($error)
+            ?? $this->extractErrorMessage($response)
+            ?? 'An error occurred with the payment gateway';
+
+        $code = $this->extractErrorField($error, ['code', 'Code', 'error_code', 'ErrorCode', 'ResultCode']);
+        $type = $this->extractErrorField($error, ['type', 'Type', 'error_type', 'ErrorType']);
+        $declineCode = $this->extractErrorField($error, ['decline_code', 'DeclineCode']);
+        $param = $this->extractErrorField($error, ['param', 'Param', 'parameter', 'Parameter']);
+        $details = [
+            'response' => $response,
+        ];
 
         switch ($statusCode) {
             case 400:
-                throw new \Yiisoft\Payments\Exceptions\InvalidRequestException(
+                throw new InvalidRequestException(
                     $message,
                     $code,
                     $type,
                     $declineCode,
                     $param,
+                    $details,
                     $statusCode
                 );
-            // Add more specific exceptions as needed
             default:
-                throw new \Yiisoft\Payments\Exceptions\PaymentException(
+                throw new PaymentException(
                     $message,
                     $code,
                     $type,
                     $declineCode,
                     $param,
+                    $details,
                     $statusCode
                 );
         }
     }
+
+    private function extractErrorMessage(array $payload): ?string
+    {
+        $message = $this->extractErrorField(
+            $payload,
+            ['message', 'Message', 'description', 'Description', 'detail', 'Detail', 'title', 'Title', 'error_description', 'error_message', 'Error']
+        );
+
+        if ($message !== null && $message !== '') {
+            return $message;
+        }
+
+        $errors = $payload['errors'] ?? $payload['Errors'] ?? null;
+        if (is_array($errors) && $errors !== []) {
+            $first = reset($errors);
+            if (is_array($first)) {
+                return $this->extractErrorMessage($first);
+            }
+
+            if (is_scalar($first)) {
+                return (string) $first;
+            }
+        }
+
+        $error = $payload['error'] ?? null;
+        if (is_scalar($error) && $error !== '') {
+            return (string) $error;
+        }
+
+        return null;
+    }
+
+    /**
+     * @param list<string> $keys
+     */
+    private function extractErrorField(array $payload, array $keys): ?string
+    {
+        foreach ($keys as $key) {
+            if (!array_key_exists($key, $payload)) {
+                continue;
+            }
+
+            $value = $payload[$key];
+            if (is_scalar($value) && $value !== '') {
+                return (string) $value;
+            }
+        }
+
+        return null;
+    }
 }
diff --git a/src/Gateways/PayPalGateway.php b/src/Gateways/PayPalGateway.php
index a308934..2f947d5 100644
--- a/src/Gateways/PayPalGateway.php
+++ b/src/Gateways/PayPalGateway.php
@@ -60,6 +60,9 @@ protected function getBaseUri(): string
      *
      * This method returns the given model with an assigned ID if it doesn't have one. No API call is made.
      * The returned ID is stable only within the calling application (store it yourself if needed).
+     * 
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public PayPal API.
      */
     public function createCustomer(Customer $customer): Customer
     {
@@ -83,6 +86,10 @@ public function createCustomer(Customer $customer): Customer
      *
      * This method returns a placeholder customer with the provided ID.
      */
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public PayPal API.
+     */
     public function retrieveCustomer(string $customerId): Customer
     {
         return new Customer(id: $customerId);
@@ -93,6 +100,10 @@ public function retrieveCustomer(string $customerId): Customer
      *
      * This method returns the input customer unchanged.
      */
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a standalone customer resource or customer update endpoint compatible with this interface. This operation cannot be implemented against the public PayPal API.
+     */
     public function updateCustomer(Customer $customer): Customer
     {
         return $customer;
@@ -102,6 +113,9 @@ public function updateCustomer(Customer $customer): Customer
      * PayPal does not expose a generic "Customer" resource compatible with this library's interface.
      *
      * This method is a no-op.
+     * 
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a standalone customer resource or customer deletion endpoint compatible with this interface. This operation cannot be implemented against the public PayPal API.
      */
     public function deleteCustomer(string $customerId): void
     {
@@ -119,6 +133,8 @@ public function deleteCustomer(string $customerId): void
      * Optional metadata keys used by this gateway:
      * - return_url: URL where PayPal will redirect the payer after approval (web flow)
      * - cancel_url: URL where PayPal will redirect the payer if they cancel (web flow)
+     * 
+     * @sandbox-support implemented
      */
     public function createPaymentIntent(PaymentIntent $paymentIntent): PaymentIntent
     {
@@ -170,6 +186,8 @@ public function createPaymentIntent(PaymentIntent $paymentIntent): PaymentIntent
 
     /**
      * Retrieves PayPal Order data.
+     * 
+     * @sandbox-support implemented
      */
     public function retrievePaymentIntent(string $paymentIntentId): PaymentIntent
     {
@@ -185,6 +203,9 @@ public function retrievePaymentIntent(string $paymentIntentId): PaymentIntent
      *
      * For PayPal web flows, payer approval happens outside of the API (via approval link).
      * This method simply re-fetches the current order state.
+     * 
+     * @sandbox-support partial
+     * @sandbox-reason PayPal order approval is performed by the payer on PayPal-hosted pages. The public API does not expose a separate generic confirm endpoint compatible with this interface.
      */
     public function confirmPaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
@@ -199,6 +220,8 @@ public function confirmPaymentIntent(string $paymentIntentId, array $params = []
      *
      * If you already have an authorization ID and want to capture it explicitly, pass it as:
      *   $this->capturePaymentIntent($orderId, ['authorization_id' => '...'])
+     * 
+     * @sandbox-support implemented
      */
         public function capturePaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
@@ -219,6 +242,7 @@ public function capturePaymentIntent(string $paymentIntentId, array $params = []
                     'paypal',
                     null,
                     'payment_source',
+                    null,
                     400
                 );
             }
@@ -288,7 +312,10 @@ public function capturePaymentIntent(string $paymentIntentId, array $params = []
         ]);
     }
 
-public function cancelPaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
+    /**
+     * @sandbox-support implemented
+     */
+    public function cancelPaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
         try {
             $order = $this->sendRequest(
@@ -306,6 +333,9 @@ public function cancelPaymentIntent(string $paymentIntentId, array $params = [])
      * PayPal does not expose a generic "PaymentMethod" resource compatible with this library's interface.
      *
      * This method returns the given model with an assigned ID if it doesn't have one. No API call is made.
+     * 
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a standalone generic payment-method resource compatible with this interface. This operation cannot be implemented against the public PayPal API.
      */
     public function createPaymentMethod(PaymentMethod $paymentMethod): PaymentMethod
     {
@@ -357,6 +387,9 @@ public function detachPaymentMethod(string $paymentMethodId): void
      * PayPal does not expose a generic "PaymentMethod" attachment API compatible with this library's interface.
      *
      * This method returns the payment method unchanged.
+     * 
+     * @sandbox-support not_implemented
+     * @sandbox-reason PayPal public API does not expose a generic payment-method attachment endpoint compatible with this interface. This operation cannot be implemented against the public PayPal API.
      */
     public function attachPaymentMethod(string $paymentMethodId, string $customerId): PaymentMethod
     {
@@ -370,6 +403,8 @@ public function attachPaymentMethod(string $paymentMethodId, string $customerId)
      * To use this method you must pass a capture ID either:
      * - as $paymentIntentId directly; OR
      * - as ['capture_id' => '...'] in $params
+     * 
+     * @sandbox-support implemented
      */
     public function createRefund(string $paymentIntentId, array $params = []): array
     {
@@ -440,6 +475,7 @@ protected function handleErrorResponse(array $responseData, int $statusCode): vo
             'paypal',
             null,
             $param,
+            null,
             $statusCode
         );
     }
@@ -470,6 +506,7 @@ private function getAccessToken(): string
                 'paypal',
                 null,
                 null,
+                null,
                 $response->getStatusCode()
             );
         }
diff --git a/src/Gateways/RobokassaGateway.php b/src/Gateways/RobokassaGateway.php
index c78be8f..9fc2615 100644
--- a/src/Gateways/RobokassaGateway.php
+++ b/src/Gateways/RobokassaGateway.php
@@ -78,6 +78,10 @@ protected function getBaseUri(): string
     // Customer and PaymentMethod operations (no-op placeholders)
     // ---------------------------------------------------------------------
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function createCustomer(Customer $customer): Customer
     {
         if ($customer->id !== null) {
@@ -95,21 +99,37 @@ public function createCustomer(Customer $customer): Customer
         );
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a standalone customer resource or customer retrieval endpoint compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function retrieveCustomer(string $customerId): Customer
     {
         return new Customer(id: $customerId);
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a standalone customer resource or customer update endpoint compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function updateCustomer(Customer $customer): Customer
     {
         return $customer;
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a standalone customer resource or customer deletion endpoint compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function deleteCustomer(string $customerId): void
     {
         // Intentionally no-op.
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a standalone generic payment-method resource compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function createPaymentMethod(PaymentMethod $paymentMethod): PaymentMethod
     {
         if ($paymentMethod->id !== null) {
@@ -141,6 +161,10 @@ public function detachPaymentMethod(string $paymentMethodId): void
         // Intentionally no-op.
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason Robokassa public API does not expose a generic payment-method attachment endpoint compatible with this interface. This operation cannot be implemented against the public Robokassa API.
+     */
     public function attachPaymentMethod(string $paymentMethodId, string $customerId): PaymentMethod
     {
         return $this->retrievePaymentMethod($paymentMethodId);
@@ -162,6 +186,8 @@ public function attachPaymentMethod(string $paymentMethodId, string $customerId)
      * Additional Robokassa-specific invoice fields can be provided via metadata:
      * - InvoiceType, ExpirationDate, Culture, Email, SuccessUrl, FailUrl, ResultUrl, Receipt, etc.
      * All metadata is passed to Robokassa as-is (except reserved keys shown above).
+     * 
+     * @sandbox-support implemented
      */
     public function createPaymentIntent(PaymentIntent $paymentIntent): PaymentIntent
     {
@@ -224,6 +250,8 @@ public function createPaymentIntent(PaymentIntent $paymentIntent): PaymentIntent
      * Returns:
      * - status: Robokassa state code (string) in metadata and mapped high-level status in PaymentIntent::status
      * - metadata.robokassa_op_key: operation key for refunds (when available)
+     * 
+     * @sandbox-support implemented
      */
     public function retrievePaymentIntent(string $paymentIntentId): PaymentIntent
     {
@@ -237,7 +265,15 @@ public function retrievePaymentIntent(string $paymentIntentId): PaymentIntent
         $code = isset($result->Code) ? (int) $result->Code : null;
         if ($code !== 0) {
             $desc = isset($result->Description) ? (string) $result->Description : 'Robokassa OpStateExt error';
-            throw new PaymentException($desc, (string) $code, 'robokassa', null, null, 400);
+            throw new PaymentException(
+                $desc,
+                (string) $code,
+                'robokassa',
+                null,
+                null,
+                null,
+                400
+            );
         }
 
         $stateCode = isset($xml->State->Code) ? (int) $xml->State->Code : null;
@@ -257,6 +293,9 @@ public function retrievePaymentIntent(string $paymentIntentId): PaymentIntent
     /**
      * For Robokassa, payer action happens on a hosted payment page.
      * This method simply re-fetches invoice state.
+     * 
+     * @sandbox-support partial
+     * @sandbox-reason Robokassa payment confirmation is performed by the payer on the hosted payment page. The public API does not expose a separate generic confirm endpoint compatible with this interface.
      */
     public function confirmPaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
@@ -266,6 +305,9 @@ public function confirmPaymentIntent(string $paymentIntentId, array $params = []
     /**
      * Robokassa does not support "capture" in the same way as card processors (it is invoice-based).
      * This method re-fetches invoice state.
+     * 
+     * @sandbox-support partial
+     * @sandbox-reason Robokassa invoice flow does not expose a separate capture endpoint compatible with this interface; payment is completed on the hosted invoice/payment page.
      */
     public function capturePaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
@@ -276,6 +318,9 @@ public function capturePaymentIntent(string $paymentIntentId, array $params = []
      * Attempts to deactivate an invoice via Invoice API.
      *
      * If the Invoice API call is not available/authorized, returns a best-effort local status.
+     * 
+     * @sandbox-support partial
+     * @sandbox-reason Robokassa invoice deactivation is not equivalent to a guaranteed generic cancel operation for this interface, so cancellation can only be provided on a best-effort basis.
      */
     public function cancelPaymentIntent(string $paymentIntentId, array $params = []): PaymentIntent
     {
@@ -344,6 +389,8 @@ public function cancelPaymentIntent(string $paymentIntentId, array $params = [])
      * If it is not provided, the gateway will call OpStateExt to obtain it.
      *
      * @return array<string,mixed>
+     * 
+     * @sandbox-support implemented
      */
     public function createRefund(string $paymentIntentId, array $params = []): array
     {
@@ -354,6 +401,7 @@ public function createRefund(string $paymentIntentId, array $params = []): array
                 'robokassa',
                 null,
                 null,
+                null,
                 500
             );
         }
@@ -371,6 +419,7 @@ public function createRefund(string $paymentIntentId, array $params = []): array
                 'robokassa',
                 null,
                 null,
+                null,
                 400
             );
         }
@@ -406,46 +455,74 @@ public function createRefund(string $paymentIntentId, array $params = []): array
     /**
      * Sends a JWT-as-body request to an endpoint that returns JSON.
      *
-     * The JWT is sent as a plain string body, without JSON encoding.
-     *
      * @return array<string,mixed>
      */
     private function sendRawJsonRequest(string $method, string $url, string $jwt): array
     {
+        $requestBody = '"' . $jwt . '"';
+
         $request = $this->requestFactory->createRequest($method, $url)
-            ->withHeader('Content-Type', 'text/plain')
+            ->withHeader('Content-Type', 'application/json')
             ->withHeader('Accept', 'application/json');
 
-        $request = $request->withBody($this->streamFactory->createStream($jwt));
+        $request = $request->withBody($this->streamFactory->createStream($requestBody));
 
         $response = $this->httpClient->sendRequest($request);
         $body = (string) $response->getBody();
         $data = json_decode($body, true);
 
         if (!is_array($data)) {
+            $this->log('error', 'Robokassa API returned a non-JSON response.', [
+                'status' => $response->getStatusCode(),
+                'body' => $body,
+            ]);
+
             throw new PaymentException(
                 'Robokassa API returned a non-JSON response.',
                 'robokassa_invalid_response',
                 'robokassa',
                 null,
                 null,
+                [
+                    'status' => $response->getStatusCode(),
+                    'response_body' => $body,
+                ],
                 $response->getStatusCode()
             );
         }
 
         if ($response->getStatusCode() >= 400) {
+            $this->log('error', 'Robokassa JSON API request failed.', [
+                'status' => $response->getStatusCode(),
+                'response' => $data,
+            ]);
             $this->handleErrorResponse($data, $response->getStatusCode());
         }
 
         // Some Robokassa endpoints return 200 even on logical failure.
-        if (isset($data['success']) && $data['success'] === false) {
-            $message = (string) ($data['message'] ?? 'Robokassa request failed.');
+        $isFailure = (isset($data['success']) && $data['success'] === false)
+            || (isset($data['Success']) && $data['Success'] === false)
+            || (isset($data['Result']) && $data['Result'] === false);
+
+        if ($isFailure) {
+            $message = $this->extractRobokassaErrorMessage($data) ?? 'Robokassa request failed.';
+            $errorCode = $this->extractRobokassaErrorCode($data) ?? 'robokassa_error';
+
+            $this->log('error', 'Robokassa logical API failure.', [
+                'status' => $response->getStatusCode(),
+                'response' => $data,
+            ]);
+
             throw new PaymentException(
                 $message,
-                (string) ($data['code'] ?? 'robokassa_error'),
+                $errorCode,
                 'robokassa',
                 null,
                 null,
+                [
+                    'status' => $response->getStatusCode(),
+                    'response' => $data,
+                ],
                 $response->getStatusCode()
             );
         }
@@ -453,6 +530,50 @@ private function sendRawJsonRequest(string $method, string $url, string $jwt): a
         return $data;
     }
 
+    private function extractRobokassaErrorMessage(array $data): ?string
+    {
+        foreach (['message', 'Message', 'description', 'Description', 'error', 'Error'] as $key) {
+            if (!array_key_exists($key, $data)) {
+                continue;
+            }
+
+            $value = $data[$key];
+            if (is_scalar($value) && $value !== '') {
+                return (string) $value;
+            }
+        }
+
+        $errors = $data['errors'] ?? $data['Errors'] ?? null;
+        if (is_array($errors) && $errors !== []) {
+            $first = reset($errors);
+            if (is_array($first)) {
+                return $this->extractRobokassaErrorMessage($first);
+            }
+
+            if (is_scalar($first) && $first !== '') {
+                return (string) $first;
+            }
+        }
+
+        return null;
+    }
+
+    private function extractRobokassaErrorCode(array $data): ?string
+    {
+        foreach (['code', 'Code', 'errorCode', 'ErrorCode'] as $key) {
+            if (!array_key_exists($key, $data)) {
+                continue;
+            }
+
+            $value = $data[$key];
+            if (is_scalar($value) && $value !== '') {
+                return (string) $value;
+            }
+        }
+
+        return null;
+    }
+
     /**
      * Sends form-encoded request to Robokassa XML API endpoint and parses XML into SimpleXMLElement.
      *
@@ -498,6 +619,7 @@ private function sendXmlRequest(string $method, string $url, array $fields): \Si
                 'robokassa',
                 null,
                 null,
+                null,
                 $response->getStatusCode()
             );
         }
diff --git a/src/Gateways/StripeGateway.php b/src/Gateways/StripeGateway.php
index 4a0c713..9a2cf02 100644
--- a/src/Gateways/StripeGateway.php
+++ b/src/Gateways/StripeGateway.php
@@ -38,13 +38,71 @@ protected function getBaseUri(): string
      */
     protected function createRequest(string $method, string $endpoint, array $data = [])
     {
-        $request = parent::createRequest($method, $endpoint, $data);
-        
-        return $request
+        $uri = rtrim($this->getBaseUri(), '/') . '/' . ltrim($endpoint, '/');
+        $request = $this->requestFactory->createRequest($method, $uri)
+            ->withHeader('Accept', 'application/json')
+            ->withHeader('User-Agent', 'PaymentGateway/' . self::API_VERSION)
             ->withHeader('Authorization', 'Bearer ' . $this->apiKey)
             ->withHeader('Stripe-Version', $this->apiVersion);
+
+        if (!empty($data)) {
+            $stream = $this->streamFactory->createStream($this->buildFormBody($data));
+            $request = $request
+                ->withBody($stream)
+                ->withHeader('Content-Type', 'application/x-www-form-urlencoded');
+        }
+
+        return $request;
+    }
+
+    /**
+     * @param array<string, mixed> $data
+     */
+    private function buildFormBody(array $data): string
+    {
+        $pairs = [];
+
+        foreach ($this->flattenFormFields($data) as $key => $value) {
+            $pairs[] = rawurlencode($key) . '=' . rawurlencode($value);
+        }
+
+        return implode('&', $pairs);
+    }
+
+    /**
+     * @param array<string, mixed> $data
+     * @return array<string, string>
+     */
+    private function flattenFormFields(array $data, string $prefix = ''): array
+    {
+        $result = [];
+
+        foreach ($data as $key => $value) {
+            if ($value === null) {
+                continue;
+            }
+
+            $field = $prefix === '' ? (string) $key : $prefix . '[' . $key . ']';
+
+            if (is_array($value)) {
+                $result += $this->flattenFormFields($value, $field);
+                continue;
+            }
+
+            if (is_bool($value)) {
+                $result[$field] = $value ? 'true' : 'false';
+                continue;
+            }
+
+            $result[$field] = (string) $value;
+        }
+
+        return $result;
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createCustomer(Customer $customer): Customer
     {
         $data = array_filter([
@@ -75,6 +133,9 @@ public function createCustomer(Customer $customer): Customer
         );
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function retrieveCustomer(string $customerId): Customer
     {
         $request = $this->createRequest('GET', "/customers/{$customerId}");
@@ -91,6 +152,9 @@ public function retrieveCustomer(string $customerId): Customer
         );
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function updateCustomer(Customer $customer): Customer
     {
         if ($customer->id === null) {
@@ -125,12 +189,18 @@ public function updateCustomer(Customer $customer): Customer
         );
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function deleteCustomer(string $customerId): void
     {
         $request = $this->createRequest('DELETE', "/customers/{$customerId}");
         $this->sendRequest($request);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createPaymentMethod(PaymentMethod $paymentMethod): PaymentMethod
     {
         $data = [
@@ -146,6 +216,9 @@ public function createPaymentMethod(PaymentMethod $paymentMethod): PaymentMethod
         return PaymentMethod::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function attachPaymentMethod(string $paymentMethodId, string $customerId): PaymentMethod
     {
         $request = $this->createRequest(
@@ -158,6 +231,9 @@ public function attachPaymentMethod(string $paymentMethodId, string $customerId)
         return PaymentMethod::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createPaymentIntent(PaymentIntent $intent): PaymentIntent
     {
         $data = array_filter([
@@ -167,6 +243,9 @@ public function createPaymentIntent(PaymentIntent $intent): PaymentIntent
             'payment_method' => $intent->paymentMethodId,
             'description' => $intent->description,
             'metadata' => $intent->metadata,
+            'capture_method' => $intent->captureMethod === null
+                ? null
+                : ($intent->captureMethod ? 'manual' : 'automatic'),
             'confirm' => $intent->confirm,
             'off_session' => $intent->offSession,
             'receipt_email' => $intent->receiptEmail,
@@ -179,6 +258,9 @@ public function createPaymentIntent(PaymentIntent $intent): PaymentIntent
         return PaymentIntent::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function confirmPaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         $request = $this->createRequest('POST', "/payment_intents/{$intentId}/confirm", $params);
@@ -186,6 +268,9 @@ public function confirmPaymentIntent(string $intentId, array $params = []): Paym
         return PaymentIntent::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function capturePaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         $request = $this->createRequest('POST', "/payment_intents/{$intentId}/capture", $params);
@@ -193,6 +278,9 @@ public function capturePaymentIntent(string $intentId, array $params = []): Paym
         return PaymentIntent::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function cancelPaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         $request = $this->createRequest('POST', "/payment_intents/{$intentId}/cancel", $params);
@@ -200,6 +288,9 @@ public function cancelPaymentIntent(string $intentId, array $params = []): Payme
         return PaymentIntent::fromArray($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createRefund(string $paymentIntentId, array $params = []): array
     {
         $params['payment_intent'] = $paymentIntentId;
@@ -215,6 +306,9 @@ public function createRefund(string $paymentIntentId, array $params = []): array
         ];
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function retrievePaymentIntent(string $intentId): PaymentIntent
     {
         $request = $this->createRequest('GET', "/payment_intents/{$intentId}");
diff --git a/src/Gateways/YooKassaGateway.php b/src/Gateways/YooKassaGateway.php
index 9336730..d71c061 100644
--- a/src/Gateways/YooKassaGateway.php
+++ b/src/Gateways/YooKassaGateway.php
@@ -45,36 +45,63 @@ protected function createRequest(string $method, string $endpoint, array $data =
         return $request;
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function createCustomer(Customer $customer): Customer
     {
         return $customer;
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function retrieveCustomer(string $customerId): Customer
     {
-        throw new \PaymentException('YooKassa API does not support retrieving customer');
+        throw new PaymentException('YooKassa API does not support retrieving customer');
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function updateCustomer(Customer $customer): Customer
     {
-        throw new \PaymentException('YooKassa API does not support updating customer');
+        throw new PaymentException('YooKassa API does not support updating customer');
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a standalone customer resource or customer CRUD endpoints compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function deleteCustomer(string $customerId): void
     {
-        throw new \PaymentException('YooKassa API does not support delete customer');
+        throw new PaymentException('YooKassa API does not support delete customer');
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a standalone generic payment-method resource compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function createPaymentMethod(PaymentMethod $paymentMethod): PaymentMethod
     {
         return $paymentMethod;
     }
 
+    /**
+     * @sandbox-support not_implemented
+     * @sandbox-reason YooKassa public API does not expose a generic payment-method attachment endpoint compatible with this interface. This operation cannot be implemented against the public YooKassa API.
+     */
     public function attachPaymentMethod(string $paymentMethodId, string $customerId): PaymentMethod
     {
         return new PaymentMethod($paymentMethodId, 'yookassa', [], $customerId);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createPaymentIntent(PaymentIntent $intent): PaymentIntent
     {
         $data = [
@@ -103,6 +130,9 @@ public function createPaymentIntent(PaymentIntent $intent): PaymentIntent
         return $this->parsePaymentIntent($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function retrievePaymentIntent(string $intentId): PaymentIntent
     {
         $request = $this->createRequest('GET', "/payments/{$intentId}");
@@ -111,11 +141,18 @@ public function retrievePaymentIntent(string $intentId): PaymentIntent
         return $this->parsePaymentIntent($response);
     }
 
+    /**
+     * @sandbox-support partial
+     * @sandbox-reason YooKassa payment flow does not expose a separate generic confirm endpoint compatible with this interface; confirmation is handled by the provider flow and subsequent capture step.
+     */
     public function confirmPaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         return $this->capturePaymentIntent($intentId,  $params);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function capturePaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         $request = $this->createRequest('POST', "/payments/{$intentId}/capture", []);
@@ -124,6 +161,9 @@ public function capturePaymentIntent(string $intentId, array $params = []): Paym
         return $this->parsePaymentIntent($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function cancelPaymentIntent(string $intentId, array $params = []): PaymentIntent
     {
         $request = $this->createRequest('POST', "/payments/{$intentId}/cancel", $params);
@@ -132,6 +172,9 @@ public function cancelPaymentIntent(string $intentId, array $params = []): Payme
         return $this->parsePaymentIntent($response);
     }
 
+    /**
+     * @sandbox-support implemented
+     */
     public function createRefund(string $paymentId, array $params = []): array
     {
         if (!array_key_exists('amount', $params) || !array_key_exists('currency', $params)) {
diff --git a/src/Models/PaymentIntent.php b/src/Models/PaymentIntent.php
index c966ae5..25ce15b 100644
--- a/src/Models/PaymentIntent.php
+++ b/src/Models/PaymentIntent.php
@@ -116,6 +116,15 @@ public static function fromArray(array $data): self
             throw new InvalidArgumentException('Currency must be a string or null');
         }
 
+        $captureMethod = $data['capture_method'] ?? $data['captureMethod'] ?? null;
+        if (is_string($captureMethod)) {
+            $captureMethod = match ($captureMethod) {
+                'manual' => true,
+                'automatic' => false,
+                default => null,
+            };
+        }
+
         return new self(
             id: $data['id'] ?? null,
             status: $data['status'] ?? null,
@@ -128,7 +137,7 @@ public static function fromArray(array $data): self
             metadata: $data['metadata'] ?? null,
             nextAction: $data['next_action'] ?? $data['nextAction'] ?? null,
             charges: $data['charges'] ?? null,
-            captureMethod: $data['capture_method'] ?? $data['captureMethod'] ?? null,
+            captureMethod: $captureMethod,
             confirm: $data['confirm'] ?? null,
             offSession: $data['off_session'] ?? $data['offSession'] ?? null,
             receiptEmail: $data['receipt_email'] ?? $data['receiptEmail'] ?? null,
diff --git a/tests/Gateways/PayPalGatewayTest.php b/tests/Gateways/PayPalGatewayTest.php
index f64ca02..8e8fad6 100644
--- a/tests/Gateways/PayPalGatewayTest.php
+++ b/tests/Gateways/PayPalGatewayTest.php
@@ -125,7 +125,7 @@ public function testCreateRefundUsesCaptureRefundV2(): void
 
         $result = $this->gateway->createRefund(
             paymentIntentId: 'CAPTURE-123',
-            amount: 1000
+            params: ['amount' => 1000]
         );
 
         $this->assertSame('RFD-123', $result['id']);
diff --git a/tests/Gateways/RobokassaGatewayTest.php b/tests/Gateways/RobokassaGatewayTest.php
index 5716bd1..bbcc68e 100644
--- a/tests/Gateways/RobokassaGatewayTest.php
+++ b/tests/Gateways/RobokassaGatewayTest.php
@@ -60,10 +60,70 @@ public function testCreatePaymentIntentCreatesInvoice(): void
         $this->assertSame('POST', $lastRequest['method']);
         $this->assertStringContainsString('InvoiceServiceWebApi/api/CreateInvoice', $lastRequest['uri']);
         $this->assertArrayHasKey('Content-Type', $lastRequest['headers']);
-        $this->assertSame('text/plain', $lastRequest['headers']['Content-Type'][0]);
+        $this->assertSame('application/json', $lastRequest['headers']['Content-Type'][0]);
 
-        // JWT has 3 dot-separated segments.
-        $this->assertCount(3, explode('.', $lastRequest['body']));
+        $this->assertStringStartsWith('"', $lastRequest['body']);
+        $this->assertStringEndsWith('"', $lastRequest['body']);
+        // JWT has 3 dot-separated segments inside quoted request body.
+        $this->assertCount(3, explode('.', trim($lastRequest['body'], '"')));
+    }
+
+
+    public function testCreatePaymentIntentIncludesApiErrorDetailsInException(): void
+    {
+        $this->httpClient->queueJsonResponse([
+            'Error' => 'Invalid signature.',
+            'ErrorCode' => 'INVALID_SIGNATURE',
+        ], 400);
+
+        $intent = new PaymentIntent(
+            id: null,
+            amount: 2500,
+            currency: 'RUB',
+            description: 'Test payment'
+        );
+
+        $this->expectException(\Yiisoft\Payments\Exceptions\InvalidRequestException::class);
+        $this->expectExceptionMessage('Invalid signature.');
+
+        try {
+            $this->gateway->createPaymentIntent($intent);
+        } catch (\Yiisoft\Payments\Exceptions\InvalidRequestException $e) {
+            $this->assertSame('INVALID_SIGNATURE', $e->errorCode);
+            $this->assertIsArray($e->details);
+            $this->assertSame('Invalid signature.', $e->details['response']['Error'] ?? null);
+            throw $e;
+        }
+    }
+
+
+    public function testCreatePaymentIntentUsesProblemDetailsTitleAsErrorMessage(): void
+    {
+        $this->httpClient->queueJsonResponse([
+            'type' => 'https://tools.ietf.org/html/rfc9110#section-15.5.16',
+            'title' => 'Unsupported Media Type',
+            'status' => 415,
+            'traceId' => 'trace-id',
+        ], 415);
+
+        $intent = new PaymentIntent(
+            id: null,
+            amount: 2500,
+            currency: 'RUB',
+            description: 'Test payment'
+        );
+
+        $this->expectException(\Yiisoft\Payments\Exceptions\PaymentException::class);
+        $this->expectExceptionMessage('Unsupported Media Type');
+
+        try {
+            $this->gateway->createPaymentIntent($intent);
+        } catch (\Yiisoft\Payments\Exceptions\PaymentException $e) {
+            $this->assertSame('https://tools.ietf.org/html/rfc9110#section-15.5.16', $e->errorType);
+            $this->assertIsArray($e->details);
+            $this->assertSame('Unsupported Media Type', $e->details['response']['title'] ?? null);
+            throw $e;
+        }
     }
 
     public function testRetrievePaymentIntentUsesOpStateExt(): void
@@ -110,7 +170,10 @@ public function testCreateRefundUsesRefundApiV2(): void
 
         $result = $this->gateway->createRefund(
             paymentIntentId: '123',
-            amount: 1000
+            params: [
+                'amount' => 1000,
+                'op_key' => 'OP-123',
+            ]
         );
 
         $this->assertTrue($result['success']);
diff --git a/tests/Gateways/StripeGatewayCaptureMethodTest.php b/tests/Gateways/StripeGatewayCaptureMethodTest.php
index 7f6b20d..2d80dff 100644
--- a/tests/Gateways/StripeGatewayCaptureMethodTest.php
+++ b/tests/Gateways/StripeGatewayCaptureMethodTest.php
@@ -52,7 +52,7 @@ public function testCreatePaymentIntentAutomaticCapture(): void
 
         $this->assertSame('pi_automatic', $result->id);
 
-        $body = json_decode($this->httpClient->lastRequest['body'], true);
+        parse_str($this->httpClient->lastRequest['body'], $body);
         $this->assertSame('automatic', $body['capture_method']);
     }
 }
diff --git a/tests/Gateways/StripeGatewayTest.php b/tests/Gateways/StripeGatewayTest.php
index 2b0cbca..d8740e9 100644
--- a/tests/Gateways/StripeGatewayTest.php
+++ b/tests/Gateways/StripeGatewayTest.php
@@ -86,6 +86,11 @@ public function testCreateCustomer(): void
         $lastRequest = $this->getLastRequest();
         $this->assertSame('POST', $lastRequest['method']);
         $this->assertStringContainsString('/customers', $lastRequest['uri']);
+        $this->assertSame('application/x-www-form-urlencoded', $lastRequest['headers']['Content-Type'][0]);
+        $this->assertStringContainsString('email=test%40example.com', $lastRequest['body']);
+        $this->assertStringContainsString('name=Test%20User', $lastRequest['body']);
+        $this->assertStringContainsString('address%5Bline1%5D=123%20Test%20St', $lastRequest['body']);
+        $this->assertStringContainsString('metadata%5Btest_meta%5D=value', $lastRequest['body']);
     }
 
     public function testCreatePaymentIntent(): void
@@ -135,6 +140,10 @@ public function testCreatePaymentIntent(): void
         $lastRequest = $this->getLastRequest();
         $this->assertSame('POST', $lastRequest['method']);
         $this->assertStringContainsString('/payment_intents', $lastRequest['uri']);
+        $this->assertSame('application/x-www-form-urlencoded', $lastRequest['headers']['Content-Type'][0]);
+        $this->assertStringNotContainsString('confirm=true', $lastRequest['body']);
+        $this->assertStringNotContainsString('off_session=false', $lastRequest['body']);
+        $this->assertStringContainsString('metadata%5Border_id%5D=12345', $lastRequest['body']);
     }
 
     public function testConfirmPaymentIntent(): void
@@ -154,7 +163,8 @@ public function testConfirmPaymentIntent(): void
         $lastRequest = $this->getLastRequest();
         $this->assertSame('POST', $lastRequest['method']);
         $this->assertStringContainsString('/payment_intents/pi_test123/confirm', $lastRequest['uri']);
-        $this->assertStringContainsString('return_url', $lastRequest['body']);
+        $this->assertSame('application/x-www-form-urlencoded', $lastRequest['headers']['Content-Type'][0]);
+        $this->assertStringContainsString('return_url=https%3A%2F%2Fexample.com%2Freturn', $lastRequest['body']);
     }
 
     public function testCreateRefund(): void
@@ -177,9 +187,11 @@ public function testCreateRefund(): void
         $lastRequest = $this->getLastRequest();
         $this->assertSame('POST', $lastRequest['method']);
         $this->assertSame('https://api.stripe.com/v1/refunds', $lastRequest['uri']);
-        $this->assertJsonStringEqualsJsonString(
-            '{"payment_intent":"pi_test123","amount":1000}',
-            $lastRequest['body']
-        );
+        $this->assertSame('application/x-www-form-urlencoded', $lastRequest['headers']['Content-Type'][0]);
+        parse_str($lastRequest['body'], $parsedBody);
+        $this->assertSame([
+            'amount' => '1000',
+            'payment_intent' => 'pi_test123',
+        ], $parsedBody);
     }
 }
diff --git a/tests/Gateways/YooKassaGatewayTest.php b/tests/Gateways/YooKassaGatewayTest.php
index c79443f..78bb52a 100644
--- a/tests/Gateways/YooKassaGatewayTest.php
+++ b/tests/Gateways/YooKassaGatewayTest.php
@@ -5,6 +5,7 @@
 namespace Yiisoft\Payments\Tests\Gateways;
 
 use PHPUnit\Framework\TestCase;
+use Yiisoft\Payments\Models\Customer;
 use Yiisoft\Payments\Models\PaymentIntent;
 use Yiisoft\Payments\Gateways\YooKassaGateway;
 use Yiisoft\Payments\Tests\Support\TestHttpClient;
@@ -42,7 +43,19 @@ private function getLastRequest(): array
         return $this->httpClient->lastRequest;
     }
 
-    public function testCreateCustomer(): void {}
+    public function testCreateCustomer(): void
+    {
+        $customer = new Customer(
+            email: 'test@example.com',
+            name: 'Test User',
+        );
+
+        $created = $this->gateway->createCustomer($customer);
+
+        $this->assertNull($created->id);
+        $this->assertSame('test@example.com', $created->email);
+        $this->assertSame('Test User', $created->name);
+    }
 
     public function testCreatePaymentIntent(): void
     {
@@ -99,7 +112,7 @@ public function testCreatePaymentIntent(): void
 
         $this->assertSame('30ae77b9-000f-5001-8000-13e0de458932', $result->id);
         $this->assertSame(10000, $result->amount);
-        $this->assertSame('rub', $result->currency);
+        $this->assertSame('RUB', $result->currency);
         $this->assertSame('Test payment', $result->description);
     }