In your profile you need to add a "lud6 or lud16" address. The format looks like a email address. The easiest way is a service like #[4] . When you install it gives you a address. There are other services for lud16 addr but you also need to make sure the service supports nip57. Basically your nostr client when you zap someone goes to the server specified and checks if it has a field named allownostr = true. If so it talks to the server and gets a fresh lightning invoice.