Fatal error: Uncaught Error: Interface "League\Config\MutableConfigurationInterface" not found in /opt/lampp/htdocs/forum/flarum/vendor/league/config/src/ConfigurationBuilderInterface.php:19 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/league/config/src/ConfigurationBuilderInterface.php on line 19