30-day free trial offer, and with weekly DM reminders to setup payment, is traditional. Just need to implement AUTH on a relay.

nostr:npub10npj3gydmv40m70ehemmal6vsdyfl7tewgvz043g54p0x23y0s8qzztl5h do you think that's a viable model?

They could come up with a gazillion new npubs, to milk that, but each new one would have zero followers and that would be painful.