Facebook’s new zero-rating initiative called Discover allows users to browse the Internet using free daily data caps. Discover is currently being tested in Peru in partnership with local telecom companies such as Bitel, Claro, Entel, and Movistar. It’s a lot similar to Free Basics in that all traffic is routed through a proxy. Discover makes use of an authentication tag (called “ickt”) that’s derived from the encryption key and a second browser identifier cookie (named “datr”), which is stored on the client.
Source: https://thehackernews.com/2020/05/facebook-discover-free-internet.html