code-review-graph/code-review-graph-main/skills/project-review/references/manual-review/payment.md

Payment Module — Manual Review Checklist

High-risk module: payment changes require human confirmation for every blocker/major fix.

• Callback idempotency: a duplicated webhook/callback does not double-charge
• Amounts stored as fixed-point (integers/cents), never floats
• Currency codes and precision handled correctly
• Provider signature / HMAC verification on callbacks
• Refund logic: correct reversal, no double-refund
• Failure path: payment timeout, declined, retry semantics
• Transaction boundary spans charge + order-state update
• Sensitive data (PAN, tokens) never logged or masked on output
• Ledger/journal entries are append-only and auditable