Using pure nostr yes, but I think what this all means is that if you have API access to your wallet and compare it with the Zap message, then you have the full end-to-end picture of what happened. IE: you could potentially use a zap on a message just like an invoice, connect to your wallet api and decide what to do. However the nostr clients will not be aware if the invoice was paid or not because that's the piece that is missing (zap confirmation type message).