Display A Global Menu For Your Multi-Site Network

/**
 * Add this function to your child theme's functions.php file which should be active site wide
 * Then log into the main site and select the menu for your "Main" menu location and it should display
 * on all subsites
 */
function my_wpex_ms_global_menu() {
  return true;
}
add_filter( 'wpex_ms_global_menu', 'my_wpex_ms_global_menu' );