Technically you could buy whoever you want gift cards and send them to them. You should not be logging into anyone’s accounts to make purchases for them as using another player's account is against ToS, but there’s nothing to say you can’t send someone money that they can use for the game. You just have to trust that they will actually use it on the game. On the whole, I’d say this is a pretty terrible idea. If they’re supposed to pay you back, how can you trust that? If they pay you up front, how do they trust you? If you’re just buying stuff for them like Santa, let me know so I can join.
There are always some people who just don't know how to operate online operations such as binding bank card accounts, so they come to ask me