Hi there!
I’m Nufar from Wix Bookings team.
We defiantly have an option for coupons today! you can read more about it here .
about the gift cards, we also have this option but it is only for new sites now. eventually, the rollout will include also existing sites. If you create a new site and add bookings you should be able to see a gift card and use it.
you can read more in this article .
tell me if you need more help:)