code: func (s *AuthService) ackMessages(c context.Context, subscription string, ackIDs []string) error {
  	if len(ackIDs) == 0 {
  		return nil
  	}
  	request := struct {
  		AckIDs []string `json:"ackIds"`
  	}{ackIDs}
  	req := internal.Request{
  		Method: "POST",
  		URL:    s.pubSubURL(subscription + ":acknowledge"),
  		Scopes: oauthScopes,
  		Body:   &request,
  	}
  	return req.Do(c)
  }
docs: // ackMessages acknowledges processing of pubsub messages.