A few additional thoughts:
The card you're using must support online transactions. Most brands of prepaid/gift cards do, but some do not.
Customers using prepaid/gift cards may be subject to some additional fraud checks at signup. If you have a normal credit or debit card, we would prefer that you use that to sign up — once you've signed up, you can always make a manual payment from a prepaid card if you want to use that up first.
Refunds to prepaid cards are kind of iffy — some of them will turn off permanently the moment that they run out of funding. If you're requesting a refund and you've used both a normal card and a prepaid one, please be specific about the exact card you want us to make the refund to!