is there a simple doc explaining how this is solved with bolt12 and still nip57 compatible?

Here's Bolt 12

https://bootstrap.bolt12.org/examples

Here's NIP 57

https://github.com/nostr-protocol/nips/blob/master/57.md

"8. Once the invoice is paid, the recipient's lnurl server MUST generate a zap receipt as described in Appendix E, and publish it to the relays specified in the zap request."

So instead its just

"8. Once the invoice is paid, the recipient's lightning node MUST generate a zap receipt as described in Appendix E, and publish it to the relays specified in the zap request."