eGift cards are nice, but they're prepaid only, meaning you have to pay upfront, and if no one redeems them, then you have to go through the trouble of reselling them or else risk losing the money.
I'm pretty sure you can generate those on-demand through an API. An alternative would be to send the reward X hours after the survey is done (where you bulk purchase the cards and send them once per day).
My target audience is basically a group of very traditional Lebanese, so cryptocurrencies and other similar "fazlaket" (as they would probably say) are a definite no-go
Depends how much they need the money.
