Popup Maker nav menu item not working

You can use something like this,

 add_filter( 'wp_nav_menu_items', 'your_custom_menu_item', 10, 2 );
    function your_custom_menu_item ( $items, $args ) {
        if ( $args->theme_location == 'Primary' ) { // change the menu location if not Primary
            $items .= '<a class="request-maintenance-open" href="#contact_form_pop">Request Maintenance</a>';
        }
        return $items;
    }