When I ordered mine, I had it shipped to a US address and used that same US address as the billing address. Had no trouble with them charging my credit card so this might be an option to try.Looks like they updated the store. It will not accept credit cards with foreign addresses anymore. I just tried to order one of the inwall AC units on the beta site, and it complains card info does not match shipment address in the US.
So, looks like only those stateside, or with a US credit card can order