on 14-10-2016 02:45 PM
@yuyan1004: That's a pretty broad question, which can't be answered without some more information.
Sometimes, certain merchants may choose to reject cards from outside of their home country as a fraud prevention measure. They also may validate the billing adress against the card, and reject the transaction because they don't match; or there could have been a communications issue with their payment gateway.
It's highly unlikely that Bankwest had any involvment in rejecting the transaction, unless the merchant is a source of frequent fraud OR the transaction triggered a fraud protection method. If the latter is the case, then you would have already received an SMS notification to your registered mobile number advising that your card has been put on hold due to suspected fraud.
If you haven't received such a notification - the best thing to do is speak to the actual merchant, and find out why they rejected the transaction.