Financial software operates under unforgiving engineering constraints: lost messages, network timeouts, or duplicate requests cannot merely return an error code—they represent real money lost, regulatory non-compliance, or double-billing lawsuits. This module teaches the battle-tested architectural patterns required to engineer fault-tolerant payment platforms and double-entry ledgers.
Across this module, you will design immutable append-only journal tables where every transfer balances debits and credits to zero, implement stateful idempotency-key state machines with atomic lock leases to deduplicate retrying clients safely, orchestrate two-phase authorization-and-capture flows across external Payment Service Providers (PSPs), and build automated T+1 settlement reconciliation pipelines that detect and quarantine sub-cent ledger drift.