In that case;

Quote Originally Posted by Rota
You need to call the number on the back of the card and register it, in order to make phone order and online orders. Right now the card has no billing address. If you call the gift card company, they can apply your address to be the billing address associated with the card, even though there is no actual bill.

I had the same issue, when I tried to use a Visa gift card to pay for an Amazon.com order.