Solving: ‘Undefined variable: menu_id’ in JetPack Mobile Theme Custom Menu Hi, this is a ‘Quick & Dirty’ but working Fix for the ‘Undefined variable: menu_id’ Issue in JetPack Mobile Theme Custom Menu setup. Edit the Main functions.php And this procedure need to be Repeated after each Plugin Update… Here I shows you how to do it by the Nix Command Line: sudo nano [SITEROOT]/wp-content/functions.php Just Replace [SITEROOT] with your Site’s Root Path. Search & Change The Line containing: return array( ‘primary’ => apply_filters( ‘jetpack_mobile_theme_menu’, $menu_id ) ); Ctrl+w to Search for ‘$menu_id’. And Change in: return array( ‘primary’ => apply_filters( …