Fatal error: Uncaught Error: Call to undefined function add_filter() in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-bookings/includes/class-integration-qrcode.php:8 Stack trace: #0 /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-bookings/includes/class-integration-qrcode.php(32): EVO_BO_QR->__construct() #1 {main} thrown in /users/laufgruppe-lvb/www/wordpress/wp-content/plugins/eventon-bookings/includes/class-integration-qrcode.php on line 8