Professor at the University of Toronto: Facebook issues cryptocurrency to increase user interaction with its platform

According to Wired, the issue of cryptocurrency for Facebook, University of Toronto professor Joshua Gans said that everything Facebook is doing now is to increase user interaction with its platform. If Facebook pays for the user who watches the ad, then the cryptocurrency system becomes very complicated. On the one hand, assuming that the user clicks on the ad and gets a discount on the product in this way, is the discount returned to the user by Facebook Coin, or is it provided directly by the merchant at the time of the commodity transaction? On the other hand, if merchants use Facebook Coin to pay for advertising and services, does it mean that Facebook Coin can't flow out of the system, just circulating in a closed loop?