The Problem You built an API. You want to charge per request. Your options: API keys + billing system — weeks of auth code, Stripe integration, chargeback risk Subscriptions — friction for new users, overkill for occasional callers OAuth — identity, not payment; still need billing on top What if a client could pay for exactly one call, right now, from anywhere in the world, with cryptographic proof — and your API verified it in 10 lines of code? HTTP 402: The Payment Required Protocol RFC 2616 reserved status code 402 "for future use." That future is now. The L402 protocol (built on top of HTTP 402) works like this: Client → GET /premium Server ← 402 Payment Required WWW-Authenticate: L402 macaroon="...", invoice="lnbc10n1..." Client pays Lightning invoice (via wallet or automated agent) Client → GET /premium Authorization: L402 <macaroon>:<preimage> Server verifies: SHA256(preimage) == paymentHash ✓ Server ← 200 OK (response) Enter fullscreen mode Exit fullscreen mode The cryptographic…