problems POSTing data to my WCF service - wcf

Question

I am trying to set up a simple service that will allow the user to pass in a Pickup object as XML in the body of a POST. If i set the service to receive a Stream type, i can get it to work fine, but I'm not sure what i need to change in order for it to instead of a custom type is works fine. When I tell the server to expect a Pickup type i get "Request Error. The server has encountered..."
I someone could tell me what i need to change in the server/client to get this to work i would appreciate it very much.
My data Contract
[DataContract]
public class Pickup
{
[DataMember]
public string DelZip
{ get; set; }
}
Operation Contract
[OperationContract]
[WebInvoke(Method = "POST",
UriTemplate = "/pickups",
RequestFormat = WebMessageFormat.Xml,
ResponseFormat = WebMessageFormat.Xml,
BodyStyle = WebMessageBodyStyle.Bare)]
string RequestPickup(Pickup pickup);
public string RequestPickup(Pickup pu)
{
return pu.DelZip;
}
config
<services>
<service name="TestAPI.Services.TestServices" >
<endpoint address=""
binding="webHttpBinding" behaviorConfiguration="webHttp"
contract="TestAPI.Services.ITestServices" />
</service>
</services>
<behaviors>
<endpointBehaviors>
<behavior name="webHttp">
<webHttp/>
</behavior>
</endpointBehaviors>
</behaviors>
my client code
const string url = "http://localhost:18463/TestServices.svc/pickups";
req = (HttpWebRequest)WebRequest.Create(url);
req.Method = "POST";
req.ContentType = "application/xml";
var xmlDoc = new XmlDocument { XmlResolver = null };
xmlDoc.LoadXml(#"<Pickup><DelZip>55555</DelZip></Pickup>");
string sXml = xmlDoc.InnerXml;
req.ContentLength = sXml.Length;
var sw = new StreamWriter(req.GetRequestStream());
sw.Write(sXml);
sw.Close();
res = (HttpWebResponse)req.GetResponse();
Stream responseStream = res.GetResponseStream();
var streamReader = new StreamReader(responseStream);