C# 将 Json 传递给 HTTP Post 请求

我正在尝试将 Json 字符串作为 HttpWebRequest 的参数与 URL 一起传递。请求会很好地命中方法，但每次参数都为空。我试过很多这样的例子，但没有成功：How to send json data in POST request using C#

这是将被序列化并传递的示例对象

Amount amount = new Amount
{
    currencyCode = "EUR",
    amount = 1234
}
string JsonParameters = amount.ToJson();
var result = Methods.ExecuteHttpPostRequestWithJson("http://localhost:51581/Home/Test", JsonParameters);

Json 参数正确序列化为

{"currencyCode":"EUR","amount":1234}

这是我尝试创建的方法。我尝试了多种方法，但每次最终都为空。

这是将要调用的方法

public static string ExecuteHttpPostRequestWithJson(string URL, string Json)
    {
        string result = "";
        var httpWebRequest = (HttpWebRequest)WebRequest.Create(URL);
        httpWebRequest.ContentType = "application/json";
        httpWebRequest.Method = "POST";
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;

        using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
        {;
            streamWriter.Write(Json);
            streamWriter.Flush();
            streamWriter.Close();
        }

        var httpResponse = (HttpWebResponse)httpWebRequest.GetResponse();
        using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
        {
            result = streamReader.ReadToEnd();
        }

        return result;
    }

这是正确命中的方法，但货币代码和金额的参数为空。

[HttpPost]
public JsonResult Test(string currencyCode, string amount)
{
    return Json(new
    {
        Test = "It worked"
    });
}