Multiple operations with path in Web API (edit)
When you do your get like this Get api/External/{id} web api is not sure whether to call the Get Method with no parameter or the Get Method with Parameter because of the default routing defined in your web api config I would suggest using attribute routing to fix your problem [Route("api/External/Get")] public async Task<IEnumerable> Get() [Route("api/External/Get/{id}")] public async Task Get(int value)
https://stackoverflow.com/questions/49056556/api-routes-multiple-operations-with-path
config.Routes.MapHttpRoute( name: "route2", routeTemplate: "api/{controller}/{organizationSys}/{id}", constraints: new { id = @"\d+" } // Only matches if "id" is one or more ); config.Routes.MapHttpRoute( name: "route1", routeTemplate: "api/{controller}/{organizationSys}" ); config.Routes.MapHttpRoute( name: "DefaultApi", routeTemplate: "api/{controller}" );