Issue #3486554: Payment Gateway duplicated transaction

Closes #3486554

src/PluginForm/HyperPayCopyAndPayForm.php

@@ -147,7 +147,10 @@ class HyperPayCopyAndPayForm extends BasePaymentOffsiteForm implements Container
       $request_params['shipping.postcode'] = $shipping_address->getPostalCode();
       $request_params['shipping.country'] = $shipping_address->getCountryCode();
     }
-    $request_params['merchantTransactionId'] = $order->id();
+    $payments = \Drupal::entityTypeManager()
+      ->getStorage('commerce_payment')
+      ->loadByProperties(['order_id' => $order->id()]);
+    $request_params['merchantTransactionId'] = $order->id() . '-' . count($payments) + 1;
     $checkout_id = $hyperpay_gateway->prepareCheckout($request_params);
 
     // Set the checkout ID as (temporary) remote ID. On actual payment, we will