protected void Application_Start() { AreaRegistration.RegisterAllAreas(); WebApiConfig.Register(GlobalConfiguration.Configuration); FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); RouteConfig.RegisterRoutes(RouteTable.Routes); BundleConfig.RegisterBundles(BundleTable.Bundles); GlobalConfiguration.Configuration.Formatters.JsonFormatter.MediaTypeMappings.Add(new QueryStringMapping("format", "json", "application/json")); GlobalConfiguration.Configuration.Formatters.XmlFormatter.MediaTypeMappings.Add(new QueryStringMapping("format", "xml", "application/xml")); var twilioFormatter = new TwilioMLXmlMediaTypeFormatter(); twilioFormatter.MediaTypeMappings.Add(new QueryStringMapping("format", "twiml", "application/xml")); GlobalConfiguration.Configuration.Formatters.Add(twilioFormatter); }