var resp = new HttpResponseMessage(HttpStatusCode.NotFound)
                {
                    Content = new StringContent(JsonConvert.SerializeObject("Code has been not found"), Encoding.UTF8, "application/json"),
                    ReasonPhrase = "Code Not Found",
                };
                return resp;

var resp = new HttpResponseMessage(HttpStatusCode.NotFound)
                {
                    Content = new StringContent(JsonConvert.SerializeObject("Code has been not found"), Encoding.UTF8, "application/json"),
                    ReasonPhrase = "Code Not Found",
                };
                return resp;

{
  "version": "1.1",
  "content": {
    "headers": [
      {
        "key": "Content-Type",
        "value": [
          "application/json; charset=utf-8"
        ]
      }
    ]
  },
  "statusCode": 404,
  "reasonPhrase": "Code Not Found",
  "headers": [],
  "trailingHeaders": [],
  "requestMessage": null,
  "isSuccessStatusCode": false
}

{
  "version": "1.1",
  "content": {
    "headers": [
      {
        "key": "Content-Type",
        "value": [
          "application/json; charset=utf-8"
        ]
      }
    ]
  },
  "statusCode": 404,
  "reasonPhrase": "Code Not Found",
  "headers": [],
  "trailingHeaders": [],
  "requestMessage": null,
  "isSuccessStatusCode": false
}