Hi Aaron,

Yes you are completely right, the order of the parameters do matter although from the reference guide there is no way of infering that. This is my code edited..

"transactionRequest": {
                            "transactionType": "authCaptureTransaction",
                            "amount": "20.00",
                             "order": {
                                "invoiceNumber": "5554446655564"
                            },
                            "customer": {
                                "email": "bmcmanus@mail.com"
                            },
                            "billTo": {
                                "firstName": "Ellen",
                                "lastName": "Johnson",
                                "company": "Souveniropolis",
                                "address": "14 Main Street",
                                "city": "Pecan Springs",
                                "state": "TX",
                                "zip": "44628",
                                "country": "USA"
                            }
                        },

Thanks!!!