diff --git a/lib/API/MP/v1/CustomFields.php b/lib/API/MP/v1/CustomFields.php
index ea76c55955..3082de1e47 100644
--- a/lib/API/MP/v1/CustomFields.php
+++ b/lib/API/MP/v1/CustomFields.php
@@ -67,7 +67,7 @@ class CustomFields {
     try {
       $customField = $this->customFieldsRepository->createOrUpdate($this->customFieldsDataSanitizer->sanitize($data));
     } catch (\Exception $e) {
-      throw new APIException('Failed to save a new subscriber field ' . join(', ', $e->getMessage()), APIException::FAILED_TO_SAVE_SUBSCRIBER_FIELD);
+      throw new APIException('Failed to save a new subscriber field ' . $e->getMessage(), APIException::FAILED_TO_SAVE_SUBSCRIBER_FIELD);
     }
     $customField = $this->customFieldsRepository->findOneById($customField->getId());
     if (!$customField instanceof CustomFieldEntity) {
diff --git a/tests/integration/API/MP/APITest.php b/tests/integration/API/MP/APITest.php
index 366a12d3e1..48d60e9e5e 100644
--- a/tests/integration/API/MP/APITest.php
+++ b/tests/integration/API/MP/APITest.php
@@ -6,7 +6,6 @@ use Codeception\Stub;
 use Codeception\Stub\Expected;
 use Codeception\Util\Fixtures;
 use MailPoet\API\MP\v1\CustomFields;
-use MailPoet\CustomFields\ApiDataSanitizer;
 use MailPoet\CustomFields\CustomFieldsRepository;
 use MailPoet\Entities\CustomFieldEntity;
 use MailPoet\Models\ScheduledTask;
diff --git a/tests/integration/API/MP/CustomFieldsTest.php b/tests/integration/API/MP/CustomFieldsTest.php
index eaba21b68f..a59f37de05 100644
--- a/tests/integration/API/MP/CustomFieldsTest.php
+++ b/tests/integration/API/MP/CustomFieldsTest.php
@@ -3,6 +3,7 @@
 namespace MailPoet\Test\API\MP;
 
 use MailPoet\API\MP\v1\API;
+use MailPoet\API\MP\v1\APIException;
 use MailPoet\CustomFields\CustomFieldsRepository;
 use MailPoet\Entities\CustomFieldEntity;
 
@@ -80,4 +81,30 @@ class CustomFieldsTest extends \MailPoetTest {
       ],
     ]);
   }
+
+  public function testItCreateNewCustomField() {
+    $response = $this->api->addSubscriberField([
+      'name' => 'text custom field',
+      'type' => 'text',
+      'params' => [
+        'required' => '1',
+        'label' => 'text custom field',
+        'date_type' => 'year_month_day',
+      ],
+    ]);
+    expect($response)->array();
+    expect($response)->hasKey('name');
+  }
+
+  public function testItFailsToCreateNewCustomField() {
+    $this->expectException(APIException::class);
+    $this->api->addSubscriberField([
+      'type' => 'text',
+      'params' => [
+        'required' => '1',
+        'label' => 'text custom field',
+        'date_type' => 'year_month_day',
+      ],
+    ]);
+  }
 }