[edsimpson]

They address that in the FAQ:

Some early Brave Origin users have asked how Brave can maintain user privacy while requiring a purchase ID (either from a Brave premium account or from the App Store / Play Store).

Brave uses a blind token protocol based on Privacy Pass, which decouples payment identity from service usage. These privacy-preserving subscription credentials allow the browser to verify you have a valid purchase of a premium product (like Origin) without learning anything about you.