Should you not be serializing the model and creating an httpconent element out of that ?
Then set the ContentType on that element
JsonSerializerSettings _settings = new JsonSerializerSettings();
JsonSerializer ser = JsonSerializer.Create(_settings);
JObject j = JObject.FromObject(model, ser);
HttpContent content = new StringContent(j.ToString());
content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
try
{
result = client.PostAsJsonAsync(url, model).Result;
}
I generally just use the client.PostAsync but it should work.
Could be wrong though !