x402

Idempotency (in payments)

A guarantee that retrying the same paid call with the same identifier results in at most one charge.

Idempotency is the critical safety property for payment systems. A buyer who's unsure whether a network blip caused their last charge to land must be able to retry without risking a second debit.

Mission Control delivers idempotency at two layers: at the wire via the x402 payment-identifier extension (vendors deduplicate by the identifier we send), and at the local DB via a UNIQUE constraint on (payment_intent_id, idempotency_key). Both must hold for a duplicate to be impossible.

Payment-Identifier (x402 extension)— An x402 extension that lets buyers attach a stable identifier to retries so vendors can deduplicate payment processing.
x402— An open standard for HTTP-native programmatic payments using stablecoins, hosted by the x402 Foundation under the Linux Foundation.