When adding a message to a zap, who has access to see that information? Is it just the person who receives the zap and only viewable in their wallet? #asknostr
Discussion
If it’s a zap, all of nostr, it can be displayed by clients along with the zap amount.
In Damus I have privacy options
What about when you go to a users profile in amethyst, for example, and send a payment with a message?
Zaps are be definition seen by whoever is connected to that relay.
if you want only the receiver to see the message you can use the note on LNURL. (if he is self sovereign, otherwise the service provider can also see it)
The problem phrasing the best possible answer to your question is around the word zap.
In my head a zap is a payment. Money moving from wallet to wallet. And i think for a lot of new Nostr users without lightning background they will associate a zap with a payment. But in reality (in the nostr world) a zap is a payment + some events around it (to tell the network about the payment).
So the answer to your question depends on the client implementation and the protocol but i'll try to summarise:
WebLN and NIP57 zaps should trigger ZapReceipt (which can be gamed) but it's telling the world you zapped. But the client can choose not to implement ZapReceipt events
With NWC and NIP-47 the wallet service is responsible for sending the payment receipt (kind 23195).
Nutzaps and NIP-61 it's the sender (client) that sends a kind 9321 to let the receiver know.
A little messy :-)