I am using a Commonwealth Bank credit card and payment has been declined

For customers using Commonwealth Bank issued Credit cards, we have found the reason why your card payment was declined is you may have two different CVV/CVNs, one for the digital version of your card, and one on the physical card. To place an order on our webiste you need to use the Physical card and CVV

This is because we recently upgraded our level of payment security.

The other requirement is the name on the card must be entered exactly the same as what is on the card. e.g if the card has Mr John Smith then Mr John Smith has to be entered. If it also has a company name then both the company name and card name has to be entered in full and exactly as per the card. 

For further information here is a link to the Commonwealth Bank website that explains which and why, scroll down to the FAQ section.

This may also apply to NAB card holders.