virtual card. some of the startup finance/banking tools can issue one for a fixed dollar amount. candidate uses it to bump their own sub for a month or top up credits.
I think “we offer a $50 (or $20 or whatever) Visa/Amex gift card as part of this interview step” is easier to admin, might skate by finance more easily, and avoids all the tech support angles of “here’s how to use our specific tooling” and concerns of them misusing your key for something nefarious.