Webhook creation issues


I am creating to create webhooks using a client i am programming. I’ve added " integration_type" with value " Webhook " as stated in the documentation, but it still returns the same error " “{“ok”:false,“error”:“integration_type is required”}” "

I am doing something quite basic so I am just not getting where is the bug:

                var client2 = new RestClient("https://api.particle.io");
                var request2 = new RestRequest("/v1/integrations" , Method.POST);
                client2.AddDefaultHeader("Authorization", string.Format("Bearer {0}", token4));
                request2.AddParameter("integration_type", "Webhook");

Thank you very much,