If you're interested in Nostr Paid Services, I've written my thoughts on approaches here - including:
1. On-demand and optionally authenticated
2. Pre-paid with authentication (and top up/extend mechanism)
3. Membership entitled and authenticated (with join mechanism and possible service feature caps or excess usage fees)
https://github.com/nostr-protocol/nips/issues/340
I'd like to collaborate to battle test these approaches, and see if we can define workflows that work for the paid services people are, and want to build on Nostr.
Feedback welcome and encouraged.