Web API configuration isn't in your RouteConfig.cs, rather your WebApiConfig.cs file. Here you will find the prefix of api/.
public static void Register(HttpConfiguration config)
{
config.MapHttpAttributeRoutes();
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
}
You'll need the prefix (api/) of some sort as there will be confusion whether its an attribute route or a normal MVC type route.
But i think the primary source of your issue is you need to be looking in the WebApiConfig.cs file.