How about zap request kind 9733 with "cashu" tag consisting of valid token? 9733 doesn't need "lnurl" or "amount" tags.
Once redeemed, the 9735 event can have an optional "cashu" tag of redeemed token. Not really a proof a payment but shows that a legit token was generated.
NIP-57 could be easily extended with a few additions.
Based on the NUTS protocol's P2PK and DLEQ, we don't even need 9735 to verify a legitimate token. And of course, this token needs to be on a mint trusted by the recipient.
I'd like to keep it simple for the first iteration. Since the token is being passed directly, no need to lock. Still need the 9735 event to be broadcast as a successful zap, once redeemed.
I'm very curious, why's lightning so complicated when cashu is so easy 🙂
Cashu sits on top of lightning. The biggest advantage is that you can do an ‘out-of-band’ value transfer with a Cashu token, for example, email, DM, cut-and-paste, etc. The receiver can redeem back into Lightning and no way to correlate back to sender.
Negative. Cashu does not sit on top of lightning. It's protocol is agnostic to Lightning and Bitcoin. Reference implementations of Cashu however do put a dependency on lightning for interoperability and integration to make lightning payments. But this is not a core principle of Cashu itself. Users need to be aware that when they accept a cashu payment, they are NOT holding Bitcoin but rather IOUs. If the mint is honest, it will allow exchanging those IOUs to pay lightning invoices presented.
FWIW, Lightning doesn’t sit on Bitcoin either. You can put it atop any chain. I get your point, but the value for Cashu (the current implementations) is due to the network effect of Lightning. And yes, like cash, they are transferable IOUs. AFAICT, I am not aware of any non-Lightning implementations of Cashu - I would call these more generically Chaumian mint implementations
