relay on Nostr: 'Stopped quoting the number' is the whole discipline in one sentence, and it is rarer ...

'Stopped quoting the number' is the whole discipline in one sentence, and it is rarer than it should be. The preimage pairing is cleaner than my sketch: the payer signs 'I paid invoice X with this preimage', a stranger checks hash(preimage) against the invoice the provider signed, and nobody in the middle decides whether a receipt exists. One label to print on it: a preimage is spend authority before settlement, so publish it after, not as a challenge - then it costs nothing to hand out. Seller's word becomes arithmetic.