diff --git a/controllers/front/addresseslist.php b/controllers/front/addresseslist.php
index 18abc5e..4903183 100644
--- a/controllers/front/addresseslist.php
+++ b/controllers/front/addresseslist.php
@@ -37,7 +37,7 @@ protected function handleOpcRequest(): array
                     'checkout/_partials/one-page-checkout/address-list',
                     [
                         'customer' => $response['customer'] ?? [],
-                        'prefix' => '',
+                        'address_type' => 'delivery',
                         'selected_address' => (int) ($response['selected_delivery_address'] ?? 0),
                     ]
                 ),
@@ -45,7 +45,7 @@ protected function handleOpcRequest(): array
                     'checkout/_partials/one-page-checkout/address-list',
                     [
                         'customer' => $response['customer'] ?? [],
-                        'prefix' => 'invoice_',
+                        'address_type' => 'invoice',
                         'selected_address' => (int) ($response['selected_invoice_address'] ?? 0),
                     ]
                 ),
diff --git a/src/Form/OnePageCheckoutForm.php b/src/Form/OnePageCheckoutForm.php
index bf7c290..265d714 100644
--- a/src/Form/OnePageCheckoutForm.php
+++ b/src/Form/OnePageCheckoutForm.php
@@ -320,8 +320,7 @@ public function submit()
             } else {
                 $invoiceAddress = $this->buildAddressFromGroup(
                     $fieldsByGroup['invoiceFields'],
-                    null,
-                    'invoice_'
+                    null
                 );
                 $invoiceAddress->id_customer = $customer->id;
                 $invoiceAddress->alias = $invoiceAddress->alias ?: $this->translator->trans(
@@ -619,7 +618,7 @@ public function getInvoiceAddress()
     {
         $fieldsByGroup = $this->mapFieldsByGroup();
 
-        return $this->buildAddressFromGroup($fieldsByGroup['invoiceFields'], null, 'invoice_');
+        return $this->buildAddressFromGroup($fieldsByGroup['invoiceFields'], null);
     }
 
     public function getTemplateVariables()
@@ -716,7 +715,10 @@ private function mapFieldsByGroup(): array
             }
 
             if ($this->isInvoiceField($key)) {
-                $fieldsByGroup['invoiceFields'][$key] = $field;
+                $strippedKey = substr($key, strlen('invoice_'));
+                $clonedField = clone $field;
+                $clonedField->setName($strippedKey);
+                $fieldsByGroup['invoiceFields'][$strippedKey] = $clonedField;
                 continue;
             }
 
@@ -838,22 +840,18 @@ private function buildCustomerFromFields(array $fields): \Customer
      * @param array<string, \FormField> $fields
      * @param int|null $idAddress
      */
-    private function buildAddressFromGroup(array $fields, $idAddress, string $prefix = ''): \Address
+    private function buildAddressFromGroup(array $fields, $idAddress): \Address
     {
         $address = new \Address($idAddress ? (int) $idAddress : null, $this->language->id);
 
         foreach ($fields as $formField) {
             $fieldName = $formField->getName();
-            $baseName = $prefix && strpos($fieldName, $prefix) === 0
-                ? substr($fieldName, strlen($prefix))
-                : $fieldName;
-
-            if (property_exists($address, $baseName)) {
-                $address->{$baseName} = $formField->getValue();
+            if (property_exists($address, $fieldName)) {
+                $address->{$fieldName} = $formField->getValue();
             }
         }
 
-        if (!isset($fields[$prefix . 'id_state'])) {
+        if (!isset($fields['id_state'])) {
             $address->id_state = 0;
         }
 
diff --git a/tests/php/Unit/Checkout/CheckoutOnePageStepRenderTest.php b/tests/php/Unit/Checkout/CheckoutOnePageStepRenderTest.php
index e0c181b..c486093 100644
--- a/tests/php/Unit/Checkout/CheckoutOnePageStepRenderTest.php
+++ b/tests/php/Unit/Checkout/CheckoutOnePageStepRenderTest.php
@@ -74,7 +74,7 @@ public function getTemplateVarConfiguration(): array
                 'additionalCustomerFields' => [],
                 'useSameAddressField' => ['value' => true],
                 'deliveryFields' => ['firstname' => ['name' => 'firstname']],
-                'invoiceFields' => ['invoice_firstname' => ['name' => 'invoice_firstname']],
+                'invoiceFields' => ['firstname' => ['name' => 'firstname']],
                 'invoiceMetaFields' => [],
                 'errors' => ['' => []],
                 'token' => 'token',
diff --git a/tests/php/Unit/Form/OnePageCheckoutFormTest.php b/tests/php/Unit/Form/OnePageCheckoutFormTest.php
index 04ba4ae..61761b5 100644
--- a/tests/php/Unit/Form/OnePageCheckoutFormTest.php
+++ b/tests/php/Unit/Form/OnePageCheckoutFormTest.php
@@ -430,7 +430,7 @@ public function testItSeparatesTemplateVariablesByBusinessOrigin(): void
         self::assertSame('opcinvariantprobe_customer_text', $templateVariables['additionalCustomerFields']['customer_probe_text']['name']);
         self::assertSame('use_same_address', $templateVariables['formFields']['use_same_address']['name']);
         self::assertSame('firstname', $templateVariables['deliveryFields']['firstname']['name']);
-        self::assertSame('invoice_address1', $templateVariables['invoiceFields']['invoice_address1']['name']);
+        self::assertSame('address1', $templateVariables['invoiceFields']['address1']['name']);
         self::assertSame('id_address_invoice', $templateVariables['invoiceMetaFields']['id_address_invoice']['name']);
     }
 
diff --git a/views/js/opc-address-modal.js b/views/js/opc-address-modal.js
index d10eea0..8b0e6a5 100644
--- a/views/js/opc-address-modal.js
+++ b/views/js/opc-address-modal.js
@@ -45,9 +45,7 @@ const BILLING_FIELDS_SELECTOR = OPC_SELECTORS.opc.billingFields;
 const DISABLED_BY_SAME_ADDRESS_ATTRIBUTE = 'data-opc-disabled-by-same-address';
 const SERVER_MANAGED_FIELDS = new Set([
   'id_country',
-  'invoice_id_country',
   'id_state',
-  'invoice_id_state',
   'use_same_address',
 ]);
 const NON_PRESERVABLE_FIELD_TYPES = new Set(['hidden', 'file', 'submit', 'button', 'image', 'reset']);
@@ -759,7 +757,7 @@ function refreshAddressesSection(options = {}) {
     payload.id_address_delivery = getAddressSectionFieldValue($addressForm, DELIVERY_SECTION_SELECTOR, DELIVERY_FIELDS_SELECTOR, 'id_address_delivery');
     payload.id_address_invoice = getAddressSectionFieldValue($addressForm, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'id_address_invoice');
     payload.id_country = getAddressSectionFieldValue($addressForm, DELIVERY_SECTION_SELECTOR, DELIVERY_FIELDS_SELECTOR, 'id_country');
-    payload.invoice_id_country = getAddressSectionFieldValue($addressForm, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'invoice_id_country');
+    payload.invoice_id_country = getAddressSectionFieldValue($addressForm, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'id_country');
   }
 
   const useSameAddress = payload.use_same_address !== '0';
@@ -776,7 +774,7 @@ function refreshAddressesSection(options = {}) {
     syncBillingSectionConstraints($addressForm, useSameAddress);
     if (!resetInlineAddressState) {
       setAddressSectionFieldValue($addressForm, DELIVERY_SECTION_SELECTOR, DELIVERY_FIELDS_SELECTOR, 'id_country', payload.id_country);
-      setAddressSectionFieldValue($addressForm, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'invoice_id_country', payload.invoice_id_country);
+      setAddressSectionFieldValue($addressForm, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'id_country', payload.invoice_id_country);
     }
 
     syncAllSavedAddressItemStyles();
diff --git a/views/js/opc-address.js b/views/js/opc-address.js
index 5209da9..cd3b9a9 100644
--- a/views/js/opc-address.js
+++ b/views/js/opc-address.js
@@ -42,9 +42,7 @@ const DISABLED_BY_SAME_ADDRESS_ATTRIBUTE = 'data-opc-disabled-by-same-address';
 
 const SERVER_MANAGED_FIELDS = new Set([
   'id_country',
-  'invoice_id_country',
   'id_state',
-  'invoice_id_state',
   'use_same_address',
 ]);
 
@@ -303,7 +301,7 @@ function seedBillingFromDelivery(addressContainer) {
     addressContainer,
     BILLING_SECTION_SELECTOR,
     BILLING_FIELDS_SELECTOR
-  ).find('[name="invoice_id_country"]').first();
+  ).find('[name="id_country"]').first();
   const previousBillingCountryValue = billingCountryField.length
     ? String(billingCountryField.val() || '')
     : '';
@@ -312,7 +310,7 @@ function seedBillingFromDelivery(addressContainer) {
     addressContainer,
     BILLING_SECTION_SELECTOR,
     BILLING_FIELDS_SELECTOR,
-    'invoice_id_country',
+    'id_country',
     deliveryCountryValue
   );
 
@@ -325,7 +323,7 @@ function seedBillingFromDelivery(addressContainer) {
     addressContainer,
     BILLING_SECTION_SELECTOR,
     BILLING_FIELDS_SELECTOR,
-    'invoice_id_state',
+    'id_state',
     deliveryStateValue
   );
 }
@@ -383,13 +381,13 @@ function refreshOpcAddressFormForCountryChange(target, selectors) {
   }
 
   // Send both country values so backend rebuilds delivery and billing sections consistently.
-  const targetName = String(target.attr('name') || '');
-  const deliveryCountryValue = targetName === 'id_country'
+  const isBillingTarget = target.closest(BILLING_SECTION_SELECTOR).length > 0;
+  const deliveryCountryValue = !isBillingTarget
     ? String(target.val() || '')
     : getAddressSectionFieldValue(addressContainer, DELIVERY_SECTION_SELECTOR, DELIVERY_FIELDS_SELECTOR, 'id_country');
-  const invoiceCountryValue = targetName === 'invoice_id_country'
+  const invoiceCountryValue = isBillingTarget
     ? String(target.val() || '')
-    : getAddressSectionFieldValue(addressContainer, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'invoice_id_country');
+    : getAddressSectionFieldValue(addressContainer, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'id_country');
   const requestData = {
     id_address_delivery: getAddressSectionFieldValue(addressContainer, DELIVERY_SECTION_SELECTOR, DELIVERY_FIELDS_SELECTOR, 'id_address_delivery'),
     id_address_invoice: getAddressSectionFieldValue(addressContainer, BILLING_SECTION_SELECTOR, BILLING_FIELDS_SELECTOR, 'id_address_invoice'),
@@ -439,7 +437,7 @@ function refreshOpcAddressFormForCountryChange(target, selectors) {
 }
 
 function handleOpcCountryChange(selectors) {
-  $('body').on('change', `${OPC_SELECTORS.opc.deliveryFields} select[name="id_country"], ${OPC_SELECTORS.opc.billingFields} select[name="invoice_id_country"]`, (event) => {
+  $('body').on('change', `${OPC_SELECTORS.opc.deliveryFields} select[name="id_country"], ${OPC_SELECTORS.opc.billingFields} select[name="id_country"]`, (event) => {
     refreshOpcAddressFormForCountryChange($(event.target), selectors);
   });
 }
diff --git a/views/js/opc-payment-list.js b/views/js/opc-payment-list.js
index d438b13..0eac90b 100644
--- a/views/js/opc-payment-list.js
+++ b/views/js/opc-payment-list.js
@@ -67,7 +67,8 @@ function buildPaymentMethodsUrl(baseUrl) {
   const idCountry = form.querySelector('[name="id_country"]')?.value
     || form.querySelector('[name="delivery_id_country"]')?.value
     || '';
-  const invoiceIdCountry = form.querySelector('[name="invoice_id_country"]')?.value || '';
+  const billingSection = form.querySelector(OPC_SELECTORS.opc.billingFields);
+  const invoiceIdCountry = (billingSection ? billingSection.querySelector('[name="id_country"]') : null)?.value || '';
   const deliveryAddressId = getSelectedSavedAddressId(OPC_SELECTORS.opc.deliveryList, 'id_address_delivery')
     || form.querySelector('[name="id_address_delivery"]')?.value
     || '';