400 error using Fiddler to hit a WCF Rest service

Question

Testing with Fiddler and a client test page, I am receiving a 400 error when making an Ajax POST to my WCF service. A GET to the same url works fine though. I set a break point in the C# code on the service, but its not even getting into the method. I need some help determining what is wrong because I have no idea at this point. A similar POST worked fine previously, but I had to rewrite my Ajax call and I'm assuming I'm missing something out of that? Very confused and frustrated.

    [OperationContract]
    [WebGet(UriTemplate = "/{appName}/{custCode}/{custUserName}/",
        ResponseFormat = WebMessageFormat.Json,
        BodyStyle = WebMessageBodyStyle.Bare)]
    IList<Url> GetUrls(string appName, string custCode, string custUserName);

    [OperationContract]
    [WebInvoke(BodyStyle = WebMessageBodyStyle.Wrapped,
        Method = "POST",
        ResponseFormat = WebMessageFormat.Json,
        UriTemplate = "/{appName}/{custCode}/{custUserName}/")]
    ResponseAction SaveDeviceInfo(string appName, string custCode, string custUserName, DeviceInfo deviceInfo);

Here is my Ajax call on the client side:

            var jsDeviceInfo = {
                deviceUuid: 'Unique660',
                deviceModel: 'Mark3',
                deviceCordova: '2.3.3',
                devicePlatform: 'Android',
                deviceVersion: '3.3.0'
            };
            $.ajax({
                type: "POST",
                contentType: "application/json; charset=utf-8",
                dataType: "json",
                url: "http://localhost:xxx/Service.svc/testApp/custCode/userId",
                data: JSON.stringify({ deviceInfo: jsDeviceInfo }),
                processdata: false,
                success: function (msg) {
                    alert(msg);
                    alert('Posted successfully');
                },
                error: function (msg) {
                    alert('Failed ' + msg.status);
                }
            });