If will work perfect if you specify only TLS in security protocol.
try { ServicePointManager.Expect100Continue = true; ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12; ServicePointManager.ServerCertificateValidationCallback = delegate { return true; }; var webClient = new WebClient(); var s = webClient.DownloadString("https://google.com"); Console.WriteLine(s); } catch (Exception ex) { Console.WriteLine(ex); } Console.ReadLine();