包含XML内容的POST请求始终为空C#

using System;
using System.IO;
using System.Net;
using System.Text;

class Program
{
    static void Main()
    {
        string xmlContent = "<root><data>Hello, World!</data></root>";
        string url = "http://example.com/api";

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
        request.Method = "POST";
        request.ContentType = "application/xml";

        byte[] xmlBytes = Encoding.UTF8.GetBytes(xmlContent);
        request.ContentLength = xmlBytes.Length;

        using (Stream requestStream = request.GetRequestStream())
        {
            requestStream.Write(xmlBytes, 0, xmlBytes.Length);
        }

        using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
        {
            using (Stream responseStream = response.GetResponseStream())
            {
                StreamReader reader = new StreamReader(responseStream);
                string responseContent = reader.ReadToEnd();
                Console.WriteLine(responseContent);
            }
        }
    }
}