How to send to topic ?

[cybersasi]

I have no problem sending message to single device with user token, but now i need to send notification to a topic what should i do?

This is my code

use NotificationChannels\FCM\FCMMessageTopic;

.....
  public function toFCM($notifiable)
    {
        return (new FCMMessageTopic())
            ->to($this->topic)
            ->notification([
                'title' => 'Notification title',
                'body' => 'Notification body',
            ]);
    }

and it return this error

FatalThrowableError in FirebaseNotification.php line 43:
Call to undefined method NotificationChannels\FCM\Exceptions\InvalidArgumentException::notification()