4xx_1.cs

public class EntityController : ApiController
{
   public SomeDto Get()
   {
     //return some DTO
   }
}

4xx_10.cs

[HttpPost]
public void DoSomething(FooDto foo)
{ 
  //....
}

4xx_11.cs

POST http://localhost:5430/api/Entity
Headers:
Accept-language: application/json

Body:
{"a":"b"}

4xx_12.cs

{"Message":"The request entity's media type 'text/plain' is not supported for this resource.","ExceptionMessage":"No MediaTypeFormatter is available to read an object of type 'FooDto' from content with media type 'text/plain'.","ExceptionType":"System.Net.Http.UnsupportedMediaTypeException","StackTrace":" at System.Net.Http.HttpContentExtensions.ReadAsAsync[T](HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)rn at System.Net.Http.HttpContentExtensions.ReadAsAsync(HttpContent content, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)rn at System.Web.Http.ModelBinding.FormatterParameterBinding.ReadContentAsync(HttpRequestMessage request, Type type, IEnumerable`1 formatters, IFormatterLogger formatterLogger, CancellationToken cancellationToken)"}

4xx_13.cs

$.postJSON = function(url, data, callback) {
return jQuery.ajax({
headers: {
'Accept': 'application/json',
'Content-Type': 'application/json'
},
'type': 'POST',
'url': url,
'data': JSON.stringify(data),
'dataType': 'json',
'success': callback
});
};

4xx_2.cs

[HttpGet]
public SomeDto A()
{
  //return some DTO
}

[HttpPost]
public SomeDto B()
{
  //return some DTO
}

4xx_3.cs

public void Blah()
{
   var x = 1;
}

4xx_4.cs

[RoutePrefix("api/foobar")]
public class EntityController : ApiController
{
  public SomeDto Get()
  {
   //return some DTO
  }
  
}

4xx_5.cs

[RoutePrefix("api/foobar")]
public class EntityController : ApiController
{

   [HttpGet, Route("")]
   public SomeDto Get()
   {
    //return some DTO
   }
}

4xx_6.cs

public class EntityController : ApiController

4xx_7.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;

namespace mypoc
{
  public static class WebApiConfig
  {
    public static void Register(HttpConfiguration config)
    {
      // Web API configuration and services
      // Web API routes
      config.MapHttpAttributeRoutes();
      config.Routes.MapHttpRoute(
        name: "DefaultApi",
        routeTemplate: "api/{controller}/{id}",
        defaults: new { id = RouteParameter.Optional }
        );
     }
  }
}

4xx_8.cs

[HttpPut, Route("foo/{field:Int}")]
public IHttpActionResult Foo(int testField)
{
   return Ok();
}

4xx_9.cs

[HttpPut, Route("foo/{field:Int}")]
public IHttpActionResult Foo(int field)
{
  return Ok();
}