What about using Binance? Letting them register them and just send them a gift card? Look at the link below.

https://www.binance.com/en/support/faq/d4f5b489c5064322826f202a2bd88d30

It has no expiry so it would depend on them when they are going to use it. It's easy to register to redeem. I think this would make it easier for both of you.