Fatal error: Uncaught Error: Call to undefined function add_filter() in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-tickets/includes/class-appearance.php:8 Stack trace: #0 /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-tickets/includes/class-appearance.php(67): evotx_appearance->__construct() #1 {main} thrown in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-tickets/includes/class-appearance.php on line 8