liwo/app/Notifications/FcmNotification.php

<?php

namespace App\Notifications;

use App\Channels\Messages\FcmMessage;
use Illuminate\Bus\Queueable;
use Illuminate\Notifications\Notification;

class FcmNotification extends Notification
{
    use Queueable;

    public $message;

    /**
     * Create a new notification instance.
     *
     * @return void
     */
    public function __construct($message)
    {
        $this->message = $message;
    }

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

    /**
     * Get the fcm representation of the notification.
     *
     * @param  mixed  $notifiable
     * @return FcmMessage
     */
    public function toFcm($notifiable)
    {
        return (new FcmMessage())
            ->data([
                'title' => $this->message['title'],
                'body' => $this->message['body'],
                'openURL' => "https://facebook.com/"
                ]);
    }

}