The status code “402 Payment Required” sat reserved and unimplemented for decades. x402 uses it as intended: the server answers 402 with the price and how to pay, the client pays, and the request succeeds. No signup, no API key, no subscription.

The reason it matters now is agents. A human happily creates an account to read one page; an agent needs a way to pay for one request, once, without a credential lifecycle. Metered access to data and APIs is the obvious first application.