Building Correct Payment Infrastructure: Webhooks, Reconciliation, and Records

Short summary

Expert with 20 years in payment systems identifies three critical mistakes that silently leak money: webhook handlers lacking replay protection and constant-time signature verification, currency calculations using float arithmetic instead of Decimal types, and reconciliation comparing totals instead of matching records individually. Provides corrective Python code patterns and introduces PayHooks, OpenRecon, and PagePDF—three open-source MIT tools implementing these fixes for Stripe, Razorpay, and other payment processors.

• •Webhook handlers must verify signatures with constant-time comparison and replay protection to prevent attacks
• •Currency calculations must use Decimal arithmetic, not floats, to avoid silent precision loss in money handling
• •Reconciliation must match records individually in two phases (exact key match, then heuristic) rather than comparing totals

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