We've decided not to include a feature where you can directly use giftcards or any other direct form of payment for reviews as we don't want to assosiate our own brand with this. Yet this is very common and we see people using the text box on the thank you page for this as a workaround.
We can do better. This will be a feature where you can leave a coupon right there, in a way better UI, with a discount for your product or service you can add in the dashboard.
There will also be a 'reward' button in the dashboard if you want to send it afterwards using email.