I recall this happening to Saifedean in Austin when he was selling books reusing a printed out bolt11 invoice. People were paying him but he didn't end up receiving the money iirc.

k00b

Right, basically the payment can be intercepted before the intended recipient gets it. So the payer would need to pay another invoice once the payee asserts they didn’t receive the funds from the original invoice 

WeAreAllSatoshi

bitcoin

What could go wrong revealing a bolt11 preimage to a payer before they've paid?

This seems to imply that it isn't the payee who can lose funds - only the payer. 

If we assume we have this payment route: Alice -> Bob -> Carol. Carol generates an invoice and reveals the preimage before Alice has sent the payment. If Bob somehow learns the preimage and Alice pays Carol through Bob, Bob can claim Alice's funds without passing along the payment to Carol. Carol will assume Alice never paid.

It seems like there's no risk to Carol and there's no harm in telling Alice the preimage ahead of time, but it is important Bob does not see it ahead of time.