Here's the gist:

1. Someone requests a Lightning invoice via your Lightning address. The requests contains extra Nostr/Zap information: https://gitea.kosmos.org/kosmos/akkounts/src/branch/master/app/controllers/lnurlpay_controller.rb#L133-L160

2. When that invoice is paid, a Zap receipt is published, so people on Nostr can see the zap: https://gitea.kosmos.org/kosmos/akkounts/src/branch/master/app/controllers/webhooks_controller.rb#L10-L19