Fatal error: Uncaught Error: Call to undefined function add_action() in /usr/local/www/wordpress/wp-content/plugins/jetpack/modules/custom-css/migrate-to-core.php:18 Stack trace: #0 /usr/local/www/wordpress/wp-content/plugins/jetpack/modules/custom-css/migrate-to-core.php(257): Jetpack_Custom_CSS_Data_Migration::add_hooks() #1 {main} thrown in /usr/local/www/wordpress/wp-content/plugins/jetpack/modules/custom-css/migrate-to-core.php on line 18