Maybe it's AW's bank that doesn't like it? Seems strange though. Did you try purchasing in a different currency? It looks like euro, dollar or sterling are available. I presume you saw this:
If the country of the cardholder is different to the one you have registered with, you should select the cardholder's Country via the 'Change Country' drop-down box below. If you are having problems with any of your recommended methods, click the 'Other Methods' Tab to select an alternative.
In the "Other Methods" tab, it looks like there's a provider call Quaife that you could use but I assume they take a cut somewhere along the line. Never heard of them so I'm not sure I'd trust it with a debit card.