There was some discussing about this with the original proposal of NIP-57. I think it was a mistake to go with LNURL rather than some nostr specific implementation. With one-sided verification of the zap, it is too easy to forge that zaps were made. It works for now and is easy to roll out, but I think longterm we'll need a better nostr specific solution.

https://github.com/nostr-protocol/nips/pull/224