Supplementary to documentation, when implementing an API there should also be a validation included, as the most important mantra is: don't trust user input.

Whatever validation you will implement in your service, you should start off by implement the IHasResponseStatus interface on your response DTO:

using ServiceStack;

public class HelloResponse : IHasResponseStatus
{
  public string Result { get; set; }
  public ResponseStatus ResponseStatus { get; set; }
}

This will guarantee that any exception will get serialized into the ResponseStatus property. Additionally, the following exceptions will adapt the HTTP status code of the request:

You can add custom mappings by adding a translation to the MapExceptionToStatusCode property of your host's config, which also supports inheritance:

using System;
using System...