402 Payment Required
Reserved for a future with money on the web — for almost three decades.
RFC 2068, in 1997, reserved 402 for the micropayment schemes the web would soon have. It did not. RFC 9110 keeps the eternal wording: reserved for future use, no standardized semantics.
While the official future fails to arrive, the code found informal jobs: Stripe returns it when a card is declined, and assorted APIs use it for exhausted paid quotas or expired plans. It is the specimen that spent thirty years in the "coming soon" display case.
HTTP/1.1 402 Payment Required
Content-Type: application/json
{"error": {"type": "card_error", "code": "card_declined"}}