test.cs

[Route("api/[controller]/merge")]
[HttpPost]
public ProcessingRequest Post(string webHookUrl) {

  ProcessingRequest request = new ProcessingRequest() {
    WebHookUrl = webHookUrl
  };

  request.Create(Url.ActionLink("Get", "DocumentProcessing", new { id = "1" }));

  // start the document processing
  Task.Run(() => TextControlProcessing.Merge(request));

  // return the status immediately
  return request;
}