WebException: The remote server returned an error: (502) Bad Gateway. This exception was originally thrown at this call stack

Hi'im getting following Error message most of time.After run the program it's working fine.sometime it's again comming.Any idea much appriciated


Error

WebException: The remote server returned an error: (502) Bad Gateway.
This exception was originally thrown at this call stack:
      System.Net.HttpWebRequest.GetResponse()
    BreezyHRapp_v2.Admin.connectAPI.getAccessToken() in connectAPI.cs
    BreezyHRapp_v2.Candidate.candidateRecords.candidateDetails(string, string) in candidateRecords.cs
      System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(System.Threading.Tasks.Task)
      System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(System.Threading.Tasks.Task)
      System.Runtime.CompilerServices.TaskAwaiter<TResult>.GetResult()
    BreezyHRapp_v2.Candidate.candidateClient.candidateDetails(string[]) in candidateClient.cs

string url = "/company/"+ companyID +"/position/"+ positionID + "/candidates";
            var request = new RestRequest(url, Method.GET);


            request.AddHeader("Content-Type", "application/json");
            request.AddHeader("cache-control", "no-cache");
            request.AddHeader("authorization", connectAPI.getAccessToken());



public static string getAccessToken()
        {
            _restClient = new restClient();
            string path = _restClient.SigninUrl;
            var httpWebRequest = (HttpWebRequest)WebRequest.Create(path);
            httpWebRequest.ContentType = "application/json";
            httpWebRequest.Method = "POST";

            using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
            {

                
                string json = JsonConvert.SerializeObject(_restClient, Formatting.Indented);


                streamWriter.Write(json);
                streamWriter.Flush();
                streamWriter.Close();
                var result = "";
                var tempAceessToken = "";
                var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
                using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                {
                    result = streamReader.ReadToEnd();
                }
                var varRestClient = JsonConvert.DeserializeObject<restClient>(result);
                tempAceessToken = varRestClient.access_token;
                return varRestClient.access_token;


            }

        }