I recently got my paid membership through giftrocket. They say they only accept US credit cards but my European card worked too. I just had to format the billing address to be as close to a US address as possible and leave the country as US. Apparently the billing address is not or only partially checked and the European-issued card no. no problem.
Gift Rocket Order confirmation JQ5BHYLTIJYL
Seems it does work with international cards although they say they only accept US cards - at least they did confirm & I also got a charge of $14.60 on my card.
Please activate my membership. Thanks!