Webclient 不喜欢 UrlEncoded 斜杠。如何让它发挥作用？

问：

我正在尝试使用 .net 2.0 webclient 将 URL 传递给 API（无法升级）。仅当编码值中没有斜杠时，webclient 调用才有效。知道它为什么失败以及如何让它工作吗？

using System.Net;
using System.Text;
using System.Web;

namespace ConsoleAppWebClient
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var client = new WebClient())
            {
                client.Encoding = Encoding.UTF8;
                client.Headers[HttpRequestHeader.Accept] = "application/xml";
                var requestUrl = HttpUtility.UrlEncode("https://www.somewebsite.com");
                var stringResult = client.DownloadString("https://localhost:12345/api/getstuff/" + requestUrl);
            }
        }
    }
}

上面不起作用，但下面的工作很好

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Text;
using System.Xml.Serialization;
using System.Web;

namespace ConsoleAppWebClient
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var client = new WebClient())
            {
                client.Encoding = Encoding.UTF8;
                client.Headers[HttpRequestHeader.Accept] = "application/xml";
                var requestUrl = HttpUtility.UrlEncode("https:www.somewebsite.com");
                var stringResult = client.DownloadString("https://localhost:12345/api/getstuff/" + requestUrl);
            }
        }
    }
}