def send_message(template_id, to, reply_to, from, subject, merge_fields = nil, view_online = false,
                                            click_tracking = true, suppress_address = false, attachments = nil, headers = nil)
      if attachments
          upload(template_id, to, reply_to, from, subject, merge_fields, view_online, click_tracking,
                                                                                    suppress_address, attachments, headers, nil, nil)
        else
          post @endpoint, params = {template_id: template_id, to: to, reply_to: reply_to, from: from,
                                    subject: subject, merge_fields: merge_fields, view_online: view_online,
                                    click_tracking: click_tracking, suppress_address: suppress_address, headers: headers}
      end
    end
def send_message(template_id, to, reply_to, from, subject, merge_fields = nil, view_online = false,
                                            click_tracking = true, suppress_address = false, attachments = nil, headers = nil)
      if attachments
          upload(template_id, to, reply_to, from, subject, merge_fields, view_online, click_tracking,
                                                                                    suppress_address, attachments, headers, nil, nil)
        else
          post @endpoint, params = {template_id: template_id, to: to, reply_to: reply_to, from: from,
                                    subject: subject, merge_fields: merge_fields, view_online: view_online,
                                    click_tracking: click_tracking, suppress_address: suppress_address, headers: headers}
      end
    end
Sends a single transactional message.

 For more information on arguments, see: [https://expresspigeon.com/kb/transactional-send].