I had a look at https://github.com/nostr-protocol/nips/blob/master/57.md .
It is not clear to me how a client verifies that a lightning invoice was paid. Does it have to verify the payment preimage from the zap receipt? How does this work? #asknostr
Discussion
There is no verification, very easy to fake. And people have done it 😂
That's the best part. It doesn't. Zaps can be faked and are faked often.