Fatal error: Uncaught Error: Call to undefined function add_filter() in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-seats/includes/class-integration-tickets.php:15 Stack trace: #0 /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-seats/includes/class-integration-tickets.php(469): evost_tickets->__construct() #1 {main} thrown in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-seats/includes/class-integration-tickets.php on line 15