I want to buy Fallout 3 for my Xbox One using a 15 dollar giftcard I recently received. I have already put the money in my account and I was wondering if I could use it to buy the game, as it is a 360 game, but is compatible with the One. Thanks!
Prepaid cards for Microsoft funds transfer into your accounts funds, which are usable across all store platforms.
You should be able to use the funds from your Xbox 360, Xbox One, or any platform (computer, tablet or phone) running Windows 8 or 10, provided you are accessing the store from the same Microsoft account.