code: func (refreshHandler *refreshCredentialsHandler) ackMessage(ack *ecsacs.IAMRoleCredentialsAckRequest) {
  	err := refreshHandler.acsClient.MakeRequest(ack)
  	if err != nil {
  		seelog.Warnf("Error 'ack'ing request with messageID: %s, error: %v", aws.StringValue(ack.MessageId), err)
  	}
  	seelog.Debugf("Acking credentials message: %s", ack.String())
  }
docs: // ackMessageId sends an IAMRoleCredentialsAckRequest to the backend