In short: the server says "you need to pay before this resource becomes available."
| Status | Meaning | Common scenario |
|---|---|---|
| 401 Unauthorized | Authentication required | Not logged in, expired token |
| 403 Forbidden | Authenticated but not allowed | Account lacks permission |
| 402 Payment Required | Payment is required | Pay-per-view, micro-payments |
| 404 Not Found | Resource missing | Broken link, content removed |
The IETF kept 402 "reserved for future use", so most production sites invented their own paywall flows instead—redirecting to checkout pages or returning 200 responses with custom overlays.
That is exactly what x402 tries to solve: converting the "payment required" signal into an automatic one-off checkout.