This talk dives into the engineering challenges of designing systems that handle payments for employees and contractors across more than 100 countries, emphasizing system design and distributed engineering principles rather than any specific product. It explores how factors like multiple payment rails, differing banking standards, currency conversions, time zones, regulatory requirements, and settlement delays impact architectural decisions. Attendees will learn practical techniques for building reliable, high-integrity financial workflows, including event-driven architectures, idempotent operations, fault-tolerant processing, robust validation, and reconciliation strategies. The session highlights how software engineers can apply distributed systems and backend design concepts to ensure correctness, scalability, and resilience in real-world global financial systems.