Start by clarifying requirements and constraints, then walk through the end-to-end flow from authorization to capture/release, emphasizing durability and idempotency. Dive into the scheduling, retry, and exactly-once mechanisms, and discuss trade-offs for partial captures and refunds.
Pro tip: Emphasize idempotency keys and state machines to ensure exactly-once semantics, and discuss how you'd handle provider failures with dead-letter queues and manual intervention.
Ask about expected scale, payment providers, SLAs, and regulatory constraints. Define the core entities: authorization, capture, refund, and their states.
Model the payment lifecycle with states like AUTHORIZED, PARTIALLY_CAPTURED, CAPTURED, RELEASED, REFUNDED. Use an append-only ledger for auditability.
Integrate with payment providers via APIs, handling idempotency keys and webhooks. Use a saga pattern to manage distributed transactions and compensations.
Use a durable job queue (e.g., database-backed or Temporal) to schedule capture/expiry jobs. Ensure jobs are persisted and retried with exponential backoff.
Support multiple partial captures up to the authorized amount. For refunds, validate against captured amount. Use dead-letter queues for failed jobs and manual resolution.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.