liwo/app/Notifications/FcmNotification.php

<?php

namespace App\Notifications;

use App\Channels\Messages\FcmMessage;
use Illuminate\Bus\Queueable;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Notifications\Messages\MailMessage;
use Illuminate\Notifications\Notification;

class FcmNotification extends Notification
{
    use Queueable;

    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct()
    {
        //
    }

    /**
     * Get the notification's delivery channels.
     *
     * @param  mixed  $notifiable
     * @return array
     */
    public function via($notifiable)
    {
        return [FcmNotification::class];
    }

    /**
     * Get the voice representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return FCMMessage
     */
    public function toFcm($notifiable)
    {
//        return (new FcmMessage())
//            ->to([])
    }

}