收到（400）错误的请求。尝试发送GCM消息时

我正在尝试通过C＃.net将消息发送到GCM服务器

我找到了一个很好的例子，我正在尝试使用

http://www.codewithasp.net/2015/11/send-message-gcm-c-sharp-single-multiple.html

问题是我收到“远程服务器返回错误：（400）错误的请求。” 每当我尝试从此行获取响应时发生错误

            WebResponse wResponse = wRequest.GetResponse();

我试图找到问题所在，将API代码从服务器更改为Android，再更改为浏览器，结果为（400）错误的请求或（401）未经授权。

不确定我在这里做错了什么，在示例中看起来非常简单直接。

非常感谢帮助

这是代码

        NotificationManager nm = new NotificationManager();
        List<string> ls = new List<string>(new string[] { "ABCDEFGHIJKLMNOPQRSTUVWXYZ" });

        nm.SendNotification(ls, " Hi.. This is a test","Hi.. Title",1);

这是课程

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Script.Serialization;
using System.Net;
using System.Text;
using System.IO;

namespace WebApplication1
{

    public class NotificationManager
    {
        private class NotificationMessage
        {
            public string Title;
            public string Message;
            public long ItemId;
        }

        public NotificationManager()
        {
            //
            // TODO: Add constructor logic here
            //
        }

        public string SendNotification(List<string> deviceRegIds, string message, string title, long id)
        {
            try
            {
                string regIds = string.Join("\",\"", deviceRegIds);

                string AppId = "AIzaSyXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
                var SenderId = "1234567890";

                NotificationMessage nm = new NotificationMessage();
                nm.Title = title;
                nm.Message = message;
                nm.ItemId = id;

                var value = new JavaScriptSerializer().Serialize(nm);
                WebRequest wRequest;
                wRequest = WebRequest.Create("https://android.googleapis.com/gcm/send");
                wRequest.Method = "post";
                wRequest.ContentType = " application/json;charset=UTF-8";
                wRequest.Headers.Add(string.Format("Authorization: key={0}", AppId));

                wRequest.Headers.Add(string.Format("Sender: id={0}", SenderId));

                string postData = "{\"collapse_key\":\"score_update\",\"time_to_live\":108,\"delay_while_idle\":true,\"data\": { \"message\" : " + "\"" + value + "\",\"time\": " + "\"" + System.DateTime.Now.ToString() + "\"},\"registration_ids\":[\"" + regIds + "\"]}";

                Byte[] bytes = Encoding.UTF8.GetBytes(postData);
                wRequest.ContentLength = bytes.Length;

                Stream stream = wRequest.GetRequestStream();
                stream.Write(bytes, 0, bytes.Length);
                stream.Close();

                WebResponse wResponse = wRequest.GetResponse();

                stream = wResponse.GetResponseStream();

                StreamReader reader = new StreamReader(stream);

                String response = reader.ReadToEnd();

                HttpWebResponse httpResponse = (HttpWebResponse)wResponse;
                string status = httpResponse.StatusCode.ToString();

                reader.Close();
                stream.Close();
                wResponse.Close();

                if (status == "")
                {
                    return response;
                }
                else
                {
                    return "";
                }
            }
            catch( Exception ex)
            {
                return ex.ToString();
            }
        }
    }
}

这是我获取API ID和发件人ID的方法