Work in progress…
The payment solution is already built (check out this article), the front is not fully ready and the authentication system needs another iteration or an audit.
Checkout brick, is my personal project, born building Fishnet. Participated with it on multiple hackathons, experimenting with anchor programs, cNFTs as invoices and token extensions to allow creating token-gated or permissionless marketplaces. Proud of my experimentation because made me learn and push myself, but now I am doubtful if that is something interesting because it increases costs vs just using a solana pay similar implementation + off-chain db.
The idea was creating pdas as a indexes (marketplaces and products) to make easier retrieving the specific marketplace transactions, with solana pay you can include the index in a transaction (outside the system/”official” front) and without proper validation after confirmation you could insert fake transactions on the db. As said, with proper validation that won’t happen, but with that program you make sure that never happens, because the validation is done on the instruction pre-cpis.