the request was aborted could not create ssl tls secure channel

            using (var client = ComHttpClient.GetHttpClient()) 

            { 

                ServicePointManager.Expect100Continue = true; 

                ServicePointManager.DefaultConnectionLimit = 9999; 

                ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12; 

                client.BaseAddress = new Uri(CommReqURL); 

  

                // Add an Accept header for JSON format. 

                client.DefaultRequestHeaders.Accept.Add( 

                    new MediaTypeWithQualityHeaderValue("application/json")); 

  

                HttpRequestMessage httpRequestMessage = new HttpRequestMessage(HttpMethod.Post, operation); 

                httpRequestMessage.Headers.Add("ServeTracingData", GenerateTraceId()); 

                var jsonSettings = new JsonSerializerSettings 

                { 

                    DateFormatHandling = DateFormatHandling.MicrosoftDateFormat 

                }; 

                var requestString = JsonConvert.SerializeObject(ocapRequest, jsonSettings); 

                httpRequestMessage.Content = new StringContent(requestString, 

                    Encoding.UTF8, 

                    "application/json"); 

                HttpResponseMessage response = null; 

                try 

                { 

                    response = await client.SendAsync(httpRequestMessage); 

                } 

                catch(Exception ex) 

                { 

  

                } 

 

public static HttpClient GetHttpClient() 

        { 

            ServicePointManager.Expect100Continue = true; 

            ServicePointManager.DefaultConnectionLimit = 9999; 

            ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12; 

           
            if (!bool.Parse(ConfigurationManager.AppSettings["abc"])) 

                return new HttpClient(); 

                 

  

            var commCertSubject = ConfigurationManager.AppSettings["Certificate"]; 

            WebRequestHandler handler = new WebRequestHandler(); 

            X509Certificate2 certificate = GetStoreCertificate(commCertSubject); 

            handler.ClientCertificates.Add(certificate); 

  

            return new HttpClient(handler); 

        } 

The above piece of code I'm using to consume a web api but recently we upgraded .net framework to 4.7.1 on the server and I get an error "the request was aborted could not create ssl tls secure channel " .

My Project target framework is 4.7.1 too. The weird thing is my colleague don't get this message but I get this. I'm not sure what's wrong. Also, he don't have the below piece of code

ServicePointManager.Expect100Continue = true; ServicePointManager.DefaultConnectionLimit = 9999; ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12; 

I searched on internet and found the solution above piece of code but this is not working for me :(. I'm scratching my head since a day. Please help!