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kite = new Kite(MyAPIKey, Debug: true, Pool:20);
            kite.EnableLogging(false);
            // Generate a redirect url for local http server
            string redirectURL = string.Format("https://{0}:{1}/", IPAddress.Loopback, GetRandomUnusedPort());
            string loginURL = string.Format("{0}&redirect_url={1}", kite.GetLoginURL(), redirectURL);          
            var http = new HttpListener();
            http.Prefixes.Add(redirectURL);
            http.Start();
           
            Process.Start(new ProcessStartInfo(loginURL) { UseShellExecute = true });
          
           // not working now
            var context = Task.Run(async () => await http.GetContextAsync()).Result;
            // Send a response back to browser
            var response = context.Response;
            string responseString = string.Format("Please return to the app");
            var buffer = System.Text.Encoding.UTF8.GetBytes(responseString);
            response.ContentLength64 = buffer.Length;
            var responseOutput = response.OutputStream;
            Task responseTask = responseOutput.WriteAsync(buffer, 0, buffer.Length).ContinueWith((task) =>
            {
                responseOutput.Close();
                http.Stop();
            });
            var requestToken = context.Request.QueryString.Get("request_token");
            if (requestToken == null)
            {
                //Console.WriteLine("Login was not completed");
                return;
            }
            //Use request token to generate access token
            User user = kite.GenerateSession(requestToken, MySecret);
            // Store this locally and reuse it. This is valid for one day    
            kite.SetAccessToken(user.AccessToken);

Note : Issue reported on 16th July 2021 lasted till next day Morning only and after 5:30 am on 17th July 2021 it started working appropriately. But this time since 13th August 2021 issue is persisting and my work is stuck.
http://127.0.0.1:12345and change code tostring redirectURL = string.Format("http://{0}:{1}/", IPAddress.Loopback, 12345);Make sure not to use "https" for this setup because the "HttpListener" cannot handle SSL without proper certificates.
To help you I am attaching one more snapshot of issue using firefox.
GetRandomUnusedPortlogic and it will be fine.Thanks for the fix. It’s working now . We can close the thread .