AC-15856: Internal Server Error When Adding Gift Card product to Cart via AddProductsToCart Mutation including custom_attributesV2

Fixed error while imploding custom attribute value array in the case the array is multidimentional

Author: sumesh-GL

app/code/Magento/CatalogGraphQl/Model/Resolver/Product/ProductCustomAttributes.php

@@ -108,7 +108,10 @@ function (AttributeInterface $customAttribute) {
             }
             $attributeValue = $productData[$attributeCode] ?? "";
             if (is_array($attributeValue)) {
-                $attributeValue = implode(',', $attributeValue);
+                $attributeValue = implode(
+                    ',',
+                    $this->getFlatArrayIfArrayIsMultiDimentional($attributeValue)
+                );
             }
             $customAttributes[] = [
                 'attribute_code' => $attributeCode,
@@ -130,4 +133,24 @@ function (array $customAttribute) {
             'errors' => $productCustomAttributes['errors']
         ];
     }
+
+    /**
+     * Returns flat array if the array passed is multidimentional
+     *
+     * @param array $array
+     * @return array
+     */
+    private function getFlatArrayIfArrayIsMultiDimentional(array $array): array
+    {
+        // Check if it's a multi-dimensional array
+        $isMultiDimensional = (count($array) != count($array, COUNT_RECURSIVE));
+        if ($isMultiDimensional) {
+            $flatArray = [];
+            array_walk_recursive($array, function ($item) use (&$flatArray) {
+                $flatArray[] = $item;
+            });
+            $array = $flatArray;
+        }
+        return $array;
+    }
 }