Fatal error: Uncaught Error: Call to undefined function add_filter() in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-speakers-schedule/includes/class-integration_lists_items.php:9 Stack trace: #0 /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-speakers-schedule/includes/class-integration_lists_items.php(21): EVOSS_Int_LI->__construct() #1 {main} thrown in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-speakers-schedule/includes/class-integration_lists_items.php on line 9