code: func (m *Messenger) Attachment(to Recipient, dataType AttachmentType, url string, messagingType MessagingType, tags ...string) error {
  	response := &Response{
  		token: m.token,
  		to:    to,
  	}
  
  	return response.Attachment(dataType, url, messagingType, tags...)
  }
docs: // Attachment sends an image, sound, video or a regular file to a given recipient.