Authorization Code Flow.Geting Error (401) Unauthorized.

This is my code.I made a public sandbox account.Geting an error 401 unauthorized.

var httpWebRequest = (HttpWebRequest)WebRequest.Create("https://platform.devtest.ringcentral.com/restapi/oauth/authorize");

httpWebRequest.Method = "GET";

httpWebRequest.Headers.Add("client_id", "DShb1**********2DlM5xoA");

httpWebRequest.Headers.Add("redirect_uri", "http://localhost:505471/");

httpWebRequest.Headers.Add("response_type", "code");

httpWebRequest.Headers.Add("state", "Client state");

httpWebRequest.Headers.Add("prompt", "login");

var httpresponse = httpWebRequest.GetResponse();