I think to implement this in a client, you need to look at both of these pages...
https://github.com/nostr-protocol/nips/issues/1843
https://github.com/nostr-protocol/nips/pull/2063
And then look again right here: https://github.com/nostr-protocol/nips/blob/master/47.md#pay_invoice
... look at that `metadata` field
.... and then look here :
https://github.com/nostr-protocol/nips/blob/master/47.md#metadata
.. specifically at this part:
```
"nostr": {
"pubkey": "string",
"tags": [],
// ...
}, // NIP-57 (Nostr Zaps)
```