C# 微信v3退款

1.退款需要退款证书。C#都是用p12的证书，双击证书导入，密码是mch_id（商户号）

2.调用微信退款接口进行退款操作

 string  resp=string.Empty
 string cert = Server.MapPath("apiclient_cert.p12");
    string password = mch_id;（商户号）
     ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);

   //这两句特别注意

   // X509Certificate cer = new X509Certificate(cert, password);//线下发布需要添加的
      X509Certificate2 cer = new X509Certificate2(cert, password, X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.MachineKeySet);//线上发        布需要添加

    HttpWebRequest webrequest = (HttpWebRequest)HttpWebRequest.Create(url);
         webrequest.ClientCertificates.Add(cer);
         webrequest.Method = "post";
         webrequest.ContentType = "application/x-www-form-urlencoded";
         webrequest.ContentLength = xml.Length;
         HttpWebResponse response = null;
    try
         {
             StreamWriter swRequestWriter = new StreamWriter(webrequest.GetRequestStream());
             swRequestWriter.Write(xml);

             if (swRequestWriter != null)
                 swRequestWriter.Close();

             response = (HttpWebResponse)webrequest.GetResponse();
             using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.Default))
             {
                 resp = reader.ReadToEnd();
             }
         }
  catch (Exception exp)
         {
             throw exp;
         }
         finally
         {
             if (response != null)
                 response.Close();
         }

分享几个退款时遇到的问题
1、退款提示:订单号非法
  原因：退款的订单号错误导致的
2、退款时提示：基础连接已关闭，或被意外关闭（验证证书的问题）
  原因： 首先要通过证书请求退款的接口，其次要把下面的这行语句

 // X509Certificate cer = new X509Certificate(cert, password);//线下发布需要添加的
 修改成这样的才可以
 X509Certificate2 cer = new X509Certificate2(cert, password, X509KeyStorageFlags.PersistKeySet | X509KeyStorageFlags.MachineKeySet);//线上发        布需要添加
3、 Miss Parameters  
  原因：传参数时，参数的名字和文档大小写不一致
4、每次退款，退款的订单号不能相同，否则无法退款