code: def send_attachment_url(self, recipient_id, attachment_type, attachment_url,
                              notification_type=NotificationType.regular):
          
          return self.send_message(recipient_id, {
              'attachment': {
                  'type': attachment_type,
                  'payload': {
                      'url': attachment_url
                  }
              }
          }, notification_type)
docs: Send an attachment to the specified recipient using URL.
          Input:
              recipient_id: recipient id to send to
              attachment_type: type of attachment (image, video, audio, file)
              attachment_url: URL of attachment
          Output:
              Response from API as <dict>