当我使用HttpWebRequest C重定向到一个url时,收到了错误的请求(400)#

HttpWebRequest request = WebRequest.Create(postUrl) as HttpWebRequest;
request.Method = "POST";
request.ContentType = contentType;
request.UserAgent = userAgent;
request.CookieContainer = new CookieContainer();
request.ContentLength = formData.Length;
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8";

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

// construct boundary etc...

var response = request.GetResponse() as HttpWebResponse;

在最后一行我得到了例外:

request 变量,我看到了 Exception.Response.ResponseUri 属性是一个重定向的url(上载成功后),它看起来像:

https://fakeurl.com/add.php?result[]=success&name[]=data_file[]

为什么?

我和小提琴手查过了,状态码是200。