payment-trading-extension

To prevent double charges and ledger drift, you must enforce per-operation idempotency keys, verify webhook signatures, and apply replay-safe deduplication for all payment-mutating operations. This ensures duplicate webhook deliveries do not result in multiple ledger entries or entitlement fraud.

Double-entry bookkeeping invariants require that every payment transaction writes matching debits and credits to an immutable ledger, ensuring balances always reconcile to zero. This prevents silent ledger drift and provides an auditable financial state for compliance.

Implement idempotency by assigning unique per-operation idempotency keys to checkout, payment intent creation, and capture workflows. The server must gate confirmation and reject duplicate mutations using the same key, ensuring retries or timeouts do not trigger duplicate charges.

A payment state machine needs exhaustive invalid-transition errors to prevent incorrect state progression during billing renewals, refunds, or disputes. Blocking undefined transitions protects against entitlement fraud and ensures server-side confirmation gating remains authoritative.

Reconcile ledger balances against provider or exchange settlement reports by implementing a reconciliation and monitoring plan with explicit alert thresholds. This detects mismatches between internal double-entry ledgers and external provider reports, preventing compliance failures.

Yes, fixed-point financial arithmetic must be used for trading order position calculations and billing proration to eliminate floating-point rounding errors. This enforces precise financial state machine calculations and maintains immutable ledger correctness.