Fatal error: Uncaught Error: Call to undefined function add_filter() in C:\xampp\htdocs\wp-content\themes\themify-ultra\themify\themify-metabox\example-functions.php:28 Stack trace: #0 {main} thrown in C:\xampp\htdocs\wp-content\themes\themify-ultra\themify\themify-metabox\example-functions.php on line 28