Fatal error: Uncaught Error: Call to undefined function add_action() in /var/www/html/web/app/mu-plugins/acorn-mvc/loader.php:19 Stack trace: #0 /var/www/html/web/app/mu-plugins/acorn-mvc.php(6): require_once() #1 {main} thrown in /var/www/html/web/app/mu-plugins/acorn-mvc/loader.php on line 19