I started with the happy path, which felt fine, but the interviewer kept steering toward reconciliation and I could feel myself getting vague.
Start by outlining the core payment flow and data model, emphasizing idempotency and state transitions. Then dive deep into reconciliation, comparing batch and streaming approaches, and detailing mismatch detection and resolution. Finally, address partial failures and disputes, showing how they integrate with the ledger and reconciliation.
Pro tip: Emphasize that reconciliation is not just about finding mismatches but also about automating resolution and learning from patterns to prevent future issues. Discuss how you'd design for observability and alerting on reconciliation metrics.
Outline the end-to-end flow: initiation, authorization, capture, refunds, and idempotency. Describe the key entities (Payment, Transaction, LedgerEntry) and their state machines.
Explain how idempotency keys are used to prevent duplicate operations, and how state transitions are managed to handle retries and partial failures.
Compare batch (e.g., daily file drops) and streaming (e.g., webhooks, message queues) reconciliation. Discuss trade-offs in latency, complexity, and reliability.
Describe how to detect mismatches (e.g., missing transactions, amount discrepancies) and the resolution process (automated retries, manual investigation, adjustments).
Explain how to manage partial failures (e.g., authorization succeeded but capture failed) and disputes (chargebacks), including ledger adjustments and communication with the processor.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.