LaravelFCM\FCMServiceProvider::register PHP Method

    public function register()
    {
        $this->app->singleton('fcm.client', function ($app) {
            return (new FCMManager($app))->driver();
        });
        $this->app->bind('fcm.group', function ($app) {
            $client = $app['fcm.client'];
            $url = $app['config']->get('fcm.http.server_group_url');
            return new FCMGroup($client, $url);
        });
        $this->app->bind('fcm.sender', function ($app) {
            $client = $app['fcm.client'];
            $url = $app['config']->get('fcm.http.server_send_url');
            return new FCMSender($client, $url);
        });
    }