SketchFab PoST WORK

        async Task RunAsync()
        {
            using (var client = new HttpClient())
            {
                client.BaseAddress = new Uri("https://sketchfab.com/");
                client.DefaultRequestHeaders.Accept.Clear();
                client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                // HTTP POST
                List<KeyValuePair<string, string>> body = new List<KeyValuePair<string, string>>
                {
                    new KeyValuePair<string, string>("code", CODE),
                    new KeyValuePair<string, string>("grant_type", "authorization_code"),
                    new KeyValuePair<string, string>("client_id", CLIENT_ID),
                    new KeyValuePair<string, string>("client_secret",CLIENT_SECRET),
                    new KeyValuePair<string, string>("redirect_uri", REDIRECT_URI)
                };
                var content = new FormUrlEncodedContent(body);
                HttpResponseMessage response = await client.PostAsync("/oauth2/token/", content);
                if (response.IsSuccessStatusCode)
                {
                    string responseStream = await response.Content.ReadAsStringAsync();
                    Console.WriteLine(responseStream);
                    Console.ReadLine();
                }
            }
        }