无法使用API​​在Pinterest上发布

Question

在Pinterest上发布图钉时，我收到504错误消息。它可以在Postman中使用，但不能在C＃中使用。

public void postPinterest(string access_token,string boardname,string note,string image_url)
            {
                try
                {

                    string uri = "https://api.pinterest.com/v1/pins";
                    System.Net.HttpWebRequest req = (System.Net.HttpWebRequest)System.Net.WebRequest.Create(uri);

                    string parameters = "access_token="
                                        + access_token
                                        + "&board="
                                        + boardname
                                        + "&note="
                                        + note
                                        + "&image_url="
                                        + image_url;

                    req.ContentType = "application/x-www-form-urlencoded";
                    req.Method = "POST";
                    byte[] bytes = Encoding.ASCII.GetBytes(parameters);
                    System.IO.Stream os = null;
                    req.ContentLength = bytes.Length;
                    os = req.GetRequestStream();
                    os.Write(bytes, 0, bytes.Length);
                    System.Net.WebResponse webResponse = req.GetResponse();
                    System.IO.Stream stream = webResponse.GetResponseStream();
                    System.IO.StreamReader reader = new System.IO.StreamReader(stream);
                    string response = reader.ReadToEnd();

                }

                catch(Exception ex)
                {
                    throw ex;
                }

            }

}