Calling service from lambda throws 403 forbidden error

                ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
                ServicePointManager.Expect100Continue = true;
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

                HttpWebRequest request = WebRequest.Create(requestUrl) as HttpWebRequest;
                request.Headers.Add("userId", iusr);
                request.Method = "GET";
                request.Credentials = System.Net.CredentialCache.DefaultCredentials;
                request.ContentType = "application/json";
                request.Accept = "application/json";

                Console.WriteLine("S3 Upload --> Debug  :  4");

                try
                {
                    HttpWebResponse myHttpWebResponse = (HttpWebResponse)request.GetResponse();
                    System.IO.StreamReader myStreamReader = new System.IO.StreamReader(myHttpWebResponse.GetResponseStream());

                    response = myStreamReader.ReadToEnd();
}