Was in here today and noticed someone at a stand validating purchases. There is a website where you can log your purchases and receipts. It then gives you an email and notification for your gift card. This then needs to be verified with your receipts again at the stand. If they run out, they can ask you to return.
Heaps of supported retailers, most food outlets and other stores but not Woolies or Coles. seems like it may be limited to apparel (fashion & accessories), beauty and/or food catering as per t&c's.