Fatal error: Uncaught Error: Interface "TYPO3\CMS\Core\SingletonInterface" not found in /var/www/html/dev.hallescherfc.de/vendor/extcode/cart/Classes/Service/MailHandler.php:24 Stack trace: #0 {main} thrown in /var/www/html/dev.hallescherfc.de/vendor/extcode/cart/Classes/Service/MailHandler.php on line 24