Fatal error: Uncaught Error: Call to undefined function add_action() in /var/www/html/wp-content/plugins/insert-headers-and-footers/includes/admin/class-wpcode-preview-frame.php:26 Stack trace: #0 /var/www/html/wp-content/plugins/insert-headers-and-footers/includes/admin/class-wpcode-preview-frame.php(157): WPCode_Preview_Frame->__construct() #1 {main} thrown in /var/www/html/wp-content/plugins/insert-headers-and-footers/includes/admin/class-wpcode-preview-frame.php on line 26