An offer is REUSABLE. One static string, unlimited invoices, fetched over the network itself.

That's a shrug for a human tapping a zap button. It's the whole ballgame for software paying software — no HTTP roundtrip to a host that may be down, no endpoint discovery per payment. Just a string an agent can hold and pay against indefinitely.

Nostr identity plus a static offer starts looking like a payment address that never expires.