MailUp REST API - How to send a transactional email message that follows a template

public static void SendTemplate()
{
  // 1) Required values
  string username = "<your_username>";
	string password = "<your_password>";

	string clientid = "<your_clientid>";
	string clientsecret = "<your_clientsecret>";

	string smtpplus_username = "<your_smtpplus_username>";
	string smtpplus_password = "<your_smtpplus_password>";
  
  // 2) Setup the MailUp Client:
	MailUpClient client = new MailUpClient(clientid, clientsecret);
	client.RetrieveAccessToken( username, password );

  // 3) prepare the input:
  TemplateDTO msg = new TemplateDTO()
  {
    TemplateId = 694,
    Subject = "Test message from template",
    From = new EmailAddressDTO() { Name = "Test User", Email = "test@mailup.it" },
    To = new List<EmailAddressDTO>() { new EmailAddressDTO() { Name = "Massimo", Email = "info@mailup.it" } },
    Cc = new List<EmailAddressDTO>(),
    Bcc = new List<EmailAddressDTO>(),
    ReplyTo = null,
    CharSet = "utf-8",
    ExtendedHeaders = null,
    Attachments = null,
    EmbeddedImages = new List<MessagePartDTO>() {
      new MessagePartDTO() {
        Filename = "Image.jpg",
        ContentId = "img001",
        Body = new byte[] { 0x01, 0x02, 0x03, 0x04 }
      }
    },
    XSmtpAPI = null,
    User = new SmtpUserDTO() { Username = smtpplus_username, Secret = smtpplus_password }
  };

  // 4) Invoke the web method:
  SendResponseDTO result = null;
  try
  {
    result = client.SendTemplate(msg);
  }
  catch (Exception ex)
  {
    Console.WriteLine("Cannot perform the operation due to " + ex.Message);
    return;
  }

  // 5) Print results:
  if (result != null)
    Console.WriteLine("Result of sending task:" + result.Message);
  else
    Console.WriteLine("An error occurred while sending template.");
}