code: func (r *Response) Attachment(dataType AttachmentType, url string, messagingType MessagingType, tags ...string) error {
  	var tag string
  	if len(tags) > 0 {
  		tag = tags[0]
  	}
  
  	m := SendStructuredMessage{
  		MessagingType: messagingType,
  		Recipient:     r.to,
  		Message: StructuredMessageData{
  			Attachment: StructuredMessageAttachment{
  				Type: dataType,
  				Payload: StructuredMessagePayload{
  					Url: url,
  				},
  			},
  		},
  		Tag: tag,
  	}
  	return r.DispatchMessage(&m)
  }
docs: // Attachment sends an image, sound, video or a regular file to a chat.