C# REST Client, HttpWebRequest

RestClient.cs

 var vm = new { label = item.PlateNo, asset = item.AssetCode, rfid = "12345678" };

  using (var client = new WebClient())
  {
      var dataString = JsonConvert.SerializeObject(vm);
      client.Headers.Add(HttpRequestHeader.ContentType, "application/json");
     // client.Headers.Add(HttpRequestHeader.Accept, "application/json");

      var res = client.UploadString(new Uri($"http://xx.xx.xx.xx/casper/api/FCS/SecondaryTag?key={key}"), "POST", dataString);

      if (res == "1")
      {

      }
  }