code: func (p *PushNotification) IsTopic() bool {
  	return (p.Platform == PlatFormAndroid && p.To != "" && strings.HasPrefix(p.To, "/topics/")) ||
  		p.Condition != ""
  }
docs: // IsTopic check if message format is topic for FCM
  // ref: https://firebase.google.com/docs/cloud-messaging/send-message#topic-http-post-request