var cli = new System.Net.Http.HttpClient();
  var requestContent = new System.Net.Http.MultipartFormDataContent("--BOUNDARY");


  requestContent.Add(new System.Net.Http.StringContent("DataToAmountVMCol"), "Amount");
  requestContent.Add(new System.Net.Http.StringContent("DataToMessageVMCol"), "Message");
  requestContent.Headers.ContentType = System.Net.Http.Headers.MediaTypeHeaderValue.Parse("multipart/form-data; boundary=--BOUNDARY");

  var url= "https://yoursystem";
  var res = cli.PostAsync(url+ "/TurnkeyRest/Post?command=Consume&id=" + TurnkeySettingFromFile.TurnKeySetting_PortalGuid, requestContent).Result;
  if (res.IsSuccessStatusCode)
  {
  }

It is important to supply a boundary token in the request and header. Otherwise, the Turnkey server will not parse the values (this is the same for all asp.net servers).