You are the a new engineer for the backend platform of an international remittance company. The company allows...

You are the a new engineer for the backend platform of an international remittance company. The company allows customers to send money globally using bank transfer, UPI, debit card, or wallet balance. The company has been operating for two years, processes millions of transactions per day across 40 countries, and is now at a point where its current architecture is causing production incidents every week. You are being brought in to redesign the payment processing and reconciliation backend from scratch. HOW A PAYMENT MOVES THROUGH THE SYSTEM Every payment follows a sequential flow through multiple internal and external systems: Initiation → Fraud and Compliance Validation → FX Rate Locking → Partner Bank Routing → Settlement → Payout Confirmation → Customer Notification Each step may involve a call to an external third-party system. A step is not complete until the external system has acknowledged it — and acknowledgement does not always arrive synchronously.