I had a plan to add this to Nowhere. Rather than DM I was going to use ephemeral messages. Serve out unique addresses from an xpub. Then just keep track of how many you have given out so you kno a how high to make the wallet gap limit. I'm the end I decoded against it as a usefull as that would be my hope is that silent payments will make that redundant for the donation use case. Still having unique addresses is useful if you want to know for certain which user has paid since they were each given a unique address. I did find one project doing this via DM as you suggest.y issue with dms is both the metadata leakage and that the messages remain on relays.

GitHub

GitHub - kdmukai/nostrpaydm: Basic proof of concept to run an on-chain bitcoin donation campaign via Nostr DMs

Basic proof of concept to run an on-chain bitcoin donation campaign via Nostr DMs - kdmukai/nostrpaydm

I really wish nostr had an edit button sometimes. 😄 but you get the idea.

Amethyst actually has. Uses kind 1010 events for this.

Mastercard and Visa must be thrilled with your POS idea, serving their agenda of controlled commerce.