Handle payment-service outages

You own a service that computes courier payouts and then submits payout requests to a downstream payment processor. What should your system do if the payment service is temporarily unavailable, timing out, or returning intermittent errors? Discuss how to preserve correctness and a good user experience, including: - idempotency for payout requests - retries with exponential backoff and jitter - when to retry synchronously vs. asynchronously - circuit breaking and fallback behavior - queue-based recovery and dead-letter handling - reconciliation after the payment service recovers - monitoring and alerting