Error - {"message": "Network error communicating with endpoint"}

Hi

  I am getting above error on below code

var client = new RestClient("api.nimbuspost.com/v1/courier/serviceability");
                client.Timeout = -1;
                var request = new RestRequest(Method.GET);
                request.AddHeader("Content-Type", "application/json");
                IRestResponse response = client.Execute(request);
                Console.WriteLine(response.Content);

Thanks