ASP.NET WebAPI returning Http 405

I have a WebApi controller

[RoutePrefix("api/invitations")]
public class InvitationsApiController : ApiController

And an action method:

[Route]
[HttpPost]
public IHttpActionResult Create([FromBody] CreateCommand command)

When i try to POST to http://host/api/invitations i get a "“405 Method Not Allowed”

But when I use another route like:

[Route("test")]
[HttpPost]
public IHttpActionResult Create([FromBody] CreateCommand command)

WebApiConfig.cs

public static void Register(HttpConfiguration config)
{
    // Web API configuration and services
    SetupFormatters(config);

    // Web API routes
    config.MapHttpAttributeRoutes();

    config.Routes.MapHttpRoute(
        name: "DefaultApi", 
        routeTemplate: "api/{controller}/{id}", 
        defaults: new { id = RouteParameter.Optional });
}

And make a POST to http://host/api/invitations/test its working. I have controllers that works just perfect when requesting to "root".

More details on Http error:

HTTP Error 405.0 - Method Not Allowed The page you are looking for cannot be displayed because an invalid method (HTTP verb) is being used.

Detailed Error Information: 
Module    DefaultDocumentModule
Notification    ExecuteRequestHandler  
Handler    StaticFile  Error
Code    0x80070001  
Requested URL   http://localhost:8008/api/invitations  
Physical Path <removed>   
Logon Method  Anonymous  
Logon User    Anonymous

Any suggestions what might be wrong?

Change your controller RoutePrefix declaration to Route at the controller level:

[Route("api/invitations")]
public class InvitationsApiController : ApiController

RoutePrefix doesn't add the route to the route table. This means, that if you want to use RoutePrefix, you'll have to prefix each action by itself, for example:

[RoutePrefix("api/invitations")]
public class InvitationsApiController : ApiController

[Route("")]
[HttpPost]
public IHttpActionResult Create([FromBody] CreateCommand command)