This is my piece of code

[HttpGet]

        [Route("attachment/{attachmentName}/{extension}")]

        [SwaggerResponse(200, "Success")]

        [SwaggerResponse(404, "Record Not Found")]

        [SwaggerResponse(401, "The User is not authorized")]

        [SwaggerResponse(400, "BadRequest")]

        [ApiAuthorizationAttribute(Privilege: "MY_SUMMARY_PAGE", Actions: (new [] { "READ","DELETE" }))]

        public async Task<IActionResult> GetAttachmentByName(string attachmentName, string extension)

        {

            _logger.LogDebug("Entering into GetAttachmentByName() in AttachmentController");

            _logger.LogInfo($"attachmentName : {attachmentName}, extension : {extension}");

            HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);

            try

            {

                List<string> imageFileFormats = new List<string>{ "png", "jpg", "jpeg", "heic" };

                if(!imageFileFormats.Contains(extension.ToLower()))

                {

                    string responseMessage = (_config["appSettings:" + "ViewAttachmentResponseMessage"]).ToString();

                    _logger.LogDebug("File formats other than image cannot be viewed currently");

                    return BadRequest(responseMessage);

                }

                if(attachmentName == string.Empty || attachmentName == null)

                {

                    _logger.LogError("Attachment Name can't be null");

                    return BadRequest("Attachment Name can't be null");

                }

                if (!Regex.IsMatch(attachmentName, @"^[a-zA-Z0-9_.-]+$"))

                {

                    _logger.LogError("Invalid attachment name format");

                    return BadRequest("Invalid attachment name format");

                }

                string compile_path = "api/attachment/{attachmentName}/{extension}";

                compile_path = compile_path.Replace("{attachmentName}", attachmentName)

                    .Replace("{extension}", extension);

                if (!Uri.TryCreate(compile_path, UriKind.RelativeOrAbsolute, out Uri requestUri))

                {

                    _logger.LogError("Invalid attachment URL");

                    return BadRequest("Invalid attachment URL");

                }

                string destinationPath = Path.Join(AppDomain.CurrentDomain.BaseDirectory, "Attachments") ;

                string fileName = attachmentName + "." + extension;

                string fullPath = Path.Join(destinationPath, fileName);

                if (!System.IO.File.Exists(fullPath))

                {

                    using (var client = new HttpClient())

                    {

                        string urlValue = Convert.ToString(_config["appSettings:" + "OldUrl"]);

                        client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", _config["appSettings:" + "OldAppToken"]);

                        client.BaseAddress = new Uri(urlValue);

                        var httpresponse = await client.GetAsync(compile_path);

                        if (httpresponse.StatusCode == System.Net.HttpStatusCode.OK)

                        {

                            using (var ms = new MemoryStream(httpresponse.Content.ReadAsByteArrayAsync().Result))

                            {

                                using (var fs = new FileStream(fullPath, FileMode.Create))

                                {

                                    ms.WriteTo(fs);

                                }                                

                            }

                        }

                        else

                        {

                             _logger.LogDebug("Response : Record not found");

                            return NotFound("Record not found");

                        }

                    }

                }

                 var image = System.IO.File.OpenRead(fullPath);

                _logger.LogDebug("Response : " + response);

                return File(image, "image/" +extension);

            }

            catch (Exception exception)

            {

                _logger.LogError(exception.ToString(), "An error occurred while getting GetAttachmentByName in AttachmentController");

                return BadRequest("Error occurred in GetAttachmentByName method");

            }

        }

I'm getting this at the line var httpresponse = await client.GetAsync(compile_path);

Please provide me with a solution