我编写了一个控制台应用程序，它调用一个 RESTful Web 服务，通过 HTTP 发送 XML 请求，返回 XML 响应。这是我目前正在使用的代码：
WebRequest wrq = WebRequest.Create("<?xml version=1.0 encoding=ISO-8859-1?>
<Request xmlns=https://sapiqa.overstock.com/api><MerchantKey>"+MerchantKey+"
</MerchantKey><AthenticationKey>"+AuthenticationKey+"</AuthenticationKey><"+APIMethod+"
/></Request>");
wrq.Method = "POST";
// Create POST data and convert it to a byte array. Strip out unnecessary text.
byte[] byteArray = Encoding.UTF8.GetBytes(URL.Replace(APIMethod, ""));
// Set the ContentType property of the WebRequest.
wrq.ContentType = "text/xml";
// Set the ContentLength property of the WebRequest.
wrq.ContentLength = byteArray.Length;
Stream dataStream = wrq.GetRequestStream();
// Write the data to the request stream.
dataStream.Write(byteArray, 0, byteArray.Length);
// Close the Stream object.
dataStream.Close();
// Get the response.
WebResponse response = wrq.GetResponse();
// Display the status.
Console.WriteLine(((HttpWebResponse)response).StatusDescription);
// Get the stream containing content returned by the server.
dataStream = response.GetResponseStream();
// Open the stream using a StreamReader for easy access.
StreamReader reader = new StreamReader(dataStream);
// Read the content.
string responseFromServer = reader.ReadToEnd();
// Display the content.
GetOrders2Response = responseFromServer;
Console.WriteLine(responseFromServer);
// Clean up the streams.
reader.Close();
dataStream.Close();
response.Close();
Console.ReadKey();
当我运行此代码时，我收到错误说明：
Invalid URI: The URI scheme is not valid.
如何通过 WebRequest 进行补救以发送格式正确的 XML 并接收 XML 响应？