3× layers
of idempotency
One integration connects your store to licensed cryptocurrency payment providers — with verified settlement, idempotent crediting and an append-only audit trail.
Funds are only ever credited on a cryptographically verified payment confirmation from the provider — never on a browser redirect.
The merchant's site sends the buyer to the Quazko cashier with the order amount. The buyer picks a payment method.
Payment is handled end-to-end by a licensed payment provider on their own checkout pages. Quazko never touches card data.
The provider's signed callback is verified, cross-checked against the provider's API, and matched against our own payment record.
A signed, idempotent delivery notifies the merchant's system exactly once — with automatic retries until acknowledged.
Every invariant below is backed by a constraint or a cryptographic check — and covered by an adversarial test suite.
A replayed confirmation can never credit twice. Deduplication happens at the database layer, so even two simultaneous callbacks resolve to exactly one credit.
Illegal state transitions are impossible. Optimistic locking means a refunded payment can never quietly return to paid, no matter the race.
The callback's amount is never trusted. Every confirmation is cross-checked against our own stored amount and currency before anything moves.
Idempotency is enforced at three layers — payment creation, inbound confirmations, and outbound crediting — backed by database constraints, not application logic alone.
Every inbound confirmation is signature-verified over raw bytes with constant-time comparison, then cross-checked against the provider's API before any state changes.
Every state transition of every payment is recorded in an append-only event log. Amounts are integer minor units end to end — floating point never touches money.
Provider credentials are stored encrypted with authenticated encryption. The platform refuses to start without a valid encryption key.
Crediting notifications are delivered with exponential backoff until acknowledged, signed with the merchant's secret so the receiving side can authenticate every message.
Merchants integrate with a single redirect or a small REST API. A reference receiver implementation is provided with the integration kit.
Send the buyer to the cashier with three parameters. Receive one signed webhook when the payment settles. That's the entire surface.