code: func (client *Client) Notify(err interface{}, extra ...interface{}) (string, error) {
  	extra = append([]interface{}{*client.context}, extra...)
  	notice := newNotice(client.Config, newError(err, 2), extra...)
  	for _, handler := range client.beforeNotifyHandlers {
  		if err := handler(notice); err != nil {
  			return "", err
  		}
  	}
  	workerErr := client.worker.Push(func() error {
  		if err := client.Config.Backend.Notify(Notices, notice); err != nil {
  			return err
  		}
  		return nil
  	})
  	if workerErr != nil {
  		client.Config.Logger.Printf("worker error: %v\n", workerErr)
  		return "", workerErr
  	}
  	return notice.Token, nil
  }
docs: // Notify reports the error err to the Honeybadger service.