Sadly, that simple concept is often misconstrued. While the URL path component is what should point directly at the server-side resource, many well-meaning developers fall into the trap of the RESTful ...

Web API doesn’t allow you to pass multiple complex objects in the method signature of a Web API controller method — you can post only a single value to a Web API action method.

Now, in order to bind parameters, Web API follows this rule: For simple types, Web API tries to get the value from the URI, and for complex types, Web API tries to get the value from the request body.