POSTing xml to Google Checkout

I'm experimenting with using Google Checkout and am having a problem posting to the checkout server. Here is my code:

XNamespace ns = XNamespace.Get("http://checkout.google.com/schema/2");

XDocument cart = new XDocument();
XElement rootElement = new XElement(ns + "checkout-shopping-cart"开发者_StackOverflow,
    new XElement("shopping-cart",
        new XElement("items",
            new XElement("item",
                new XElement("item-name", "doodad"),
                new XElement("item-description", "Description for the doodad"),
                new XElement("unit-price", 9.99, new XAttribute("currency", "GBP")),
                new XElement("quantity", 1)
            )
         )
    )
);

cart.Add(rootElement);

string authKey = "111222333444:NOTAREALKEY";
authKey = EncodeToBase64(authKey);

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://checkout.google.com/cws/v2/Merchant/111222333444/merchantCheckout");

request.Method = "POST";
byte[] byteArray = Encoding.UTF8.GetBytes(cart.ToString());
request.ContentType = "application/xml; charset=UTF-8";
request.ContentLength = byteArray.Length;
request.Headers.Add("Authorization: Basic " + authKey);
request.Accept = "application/xml; charset=UTF-8";

Stream dataStream = request.GetRequestStream();
dataStream.Write(byteArray, 0, byteArray.Length);
dataStream.Close();

HttpWebResponse response = (HttpWebResponse)request.GetResponse(); // Exception here!
dataStream = response.GetResponseStream();
StreamReader reader = new StreamReader(dataStream);
string responseText = reader.ReadToEnd();

reader.Close();
dataStream.Close();
response.Close();

When I call GetResponse(), I get a (400) Bad Request.

Any assistance on this would be gratefully received.

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Your XML looks broken as Jon Skeet points out :-). In order to further aid debugging - there may be more information about the error in the response. WebException has a Response object that might have a more detailed error message that can be read by calling its GetResponseStream() method.

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Not knowing anything about the Google Checkout API, are you sure you don't need the namespace on each of those elements?

XElement rootElement = new XElement(ns + "checkout-shopping-cart",
    new XElement(ns + "shopping-cart"),
        new XElement(ns + "items",
                     // etc

That's certainly what the Checkout API guide suggests to me - note that "xmlns=..." means that's the namespace for this element and all descendant elements unless otherwise specified.

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You still can read response message, if exception is WebException. This will give you more information on what's wrong:

try {
   response = (HttpWebResponse)request.GetResponse();
}
catch (WebException ex1) {
   response = ex1.Response();
}