支付单号：4200002525202411253451761069

System.IO.Stream s = HttpContext.Current.Request.InputStream;
int count = 0;
byte[] buffer = new byte[1024];
StringBuilder builder = new StringBuilder();
while ((count = s.Read(buffer, 0, 1024)) > 0)
{
    builder.Append(Encoding.UTF8.GetString(buffer, 0, count));
}
s.Flush();
s.Close();
s.Dispose();
var str = builder.ToString();

str为空