Fintech & Commerce

Design a Payment Gateway (Stripe clone, strict idempotency focus)

A payment processing gateway routing transactions to card networks and banks while guaranteeing exactly-once charge semantics via strict idempotency.

Core Architectural Components

Guarantees a retried charge request never results in a duplicate charge.

State machine driving a payment through authorized → captured → settled or failed.

Translates internal payment intent into the external network's protocol.

Isolates raw card data to a minimal PCI-scoped boundary.

Reliably notifies merchants of async payment state changes.

Screens transactions before authorization.

Keeps internal accounting consistent with what actually settled.

Handles transient failures without silently dropping a payment.