Fatal error: Uncaught Error: Class 'Symfony\Contracts\EventDispatcher\Event' not found in /mnt/volume_lon1_01/backend/admin/vendor/symfony/event-dispatcher/GenericEvent.php:23 Stack trace: #0 {main} thrown in /mnt/volume_lon1_01/backend/admin/vendor/symfony/event-dispatcher/GenericEvent.php on line 23