Fatal error: Uncaught Error: Class "Sabre\CardDAV\Backend\AbstractBackend" not found in /var/www/illumine/vendor/sabre/dav/lib/CardDAV/Backend/PDO.php:17 Stack trace: #0 {main} thrown in /var/www/illumine/vendor/sabre/dav/lib/CardDAV/Backend/PDO.php on line 17