Fatal error: Uncaught Error: Interface 'Sabre\DAVACL\PrincipalBackend\BackendInterface' not found in /home/malert/WebDAV/vendor/sabre/dav/lib/DAVACL/PrincipalBackend/AbstractBackend.php:16 Stack trace: #0 {main} thrown in /home/malert/WebDAV/vendor/sabre/dav/lib/DAVACL/PrincipalBackend/AbstractBackend.php on line 16