try
            {
                var client = new HttpClient();
                var queryString = HttpUtility.ParseQueryString(string.Empty);
                client.DefaultRequestHeaders.Add("Ocp-Apim-Subscription-Key", SubscriptionKey);
                    ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072 | (SecurityProtocolType)768 | SecurityProtocolType.Tls;
                var response = client.GetAsync(requestUri);
                response.Wait();
                var contentType = response.Result.Content.Headers.ContentType;
                if (response.Result.IsSuccessStatusCode &&
                            string.Equals(contentType.MediaType, "application/json", StringComparison.OrdinalIgnoreCase))
                {
                    var list = response.Result.Content.ReadAsAsync<List<AzureTranscription>>();
                    return list;
                }
else
                {
                    WriteTranscriptInfoMessageToLogFile("Error with status getting transcription result"+ response.Result.StatusCode);
                    return null;
                    //continue;
                }
            }
            catch(Exception ex)
            {                
                return null;
            }
        }
Instead of using  ServicePointManager.SecurityProtocol = (SecurityProtocolType)3072 | (SecurityProtocolType)768 | SecurityProtocolType.Tls; i tried with this also ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;