function get_main_menu ( $params ) {

    $menu_items = wp_get_nav_menu_items('main');
    $base_url = get_site_url();
    $replace = array($base_url, "/");

    foreach ($menu_items as $m) {
        $item = (object) [
            'title' => $m->title,
            'id' => $m->ID,
            'url' => $m->url,
            'slug' => str_replace($replace, "", $m->url),
        ];

        $menu[] = $item;
    }

    return $menu;

 }

add_action( 'rest_api_init', function () {

    register_rest_route( 'menus/v1', '/main',array(
    'methods'  => 'GET',
    'callback' => 'get_main_menu'
    ) );

 } );