Build a payment reconciliation job for my app: a regular check that my local records and the payment provider's records agree. Implement: a scheduled job (daily or weekly) that pulls recent charges, refunds, and subscription invoices from the provider's API and compares them against my local order and payment records; flags every mismatch in both directions (a charge at the provider with no local order, meaning fulfillment or access was never granted; a local order marked paid with no provider charge, meaning my state is lying); checks amounts and currencies match, not just existence; and reports discrepancies in a digest I actually read, with record IDs on both sides so investigation starts from the report. Keep it read-only; reconciliation reports, humans fix. Don't auto-repair mismatches by mutating local records to match the provider; the mismatch is a symptom of a bug (missed webhook, double charge, failed fulfillment) and silently patching it hides the bug. Don't alert on expected timing gaps (a charge seconds old that the webhook hasn't delivered yet); use a small lag window. Deliver: the reconciliation job with its schedule, the mismatch report format, and verification: deliberately create a mismatch in test mode (a provider-side charge with no local record) and confirm the next run reports it.