fix: declare error as error message instead of success msg

ajax/getList.php

@@ -44,7 +44,7 @@ function ($searchParams) {
         } catch (\Exception $Exception) {
             QUI\System\Log::writeException($Exception);
 
-            QUI::getMessagesHandler()->addSuccess(
+            QUI::getMessagesHandler()->addError(
                 QUI::getLocale()->get(
                     'quiqqer/coupons',
                     'message.ajax.general_error'