03 - Invalid merchant
This can be returned by Westpac when there is a problem with the merchant configuration. This can also be returned for AMEX transactions when there is a problem with the setup at American Express®. This code can be returned from an issuing bank if they don’t like the acquiring bank. An example of this would be someone trying to pay their speeding fine with an overseas credit card. The overseas issuing bank would return a 03, indicating that they wouldn’t allow the transaction over the internet for an Australian bank.