This question evaluates system design and financial-systems competencies, including distributed systems, transactional integrity, ledger and money-movement models, API and data-model design, failure handling, security, compliance, and operational concerns like scalability and auditability.
Design a payment system that supports moving money between users and paying merchants.
Your design should cover:
Assume the system may integrate with external payment rails/providers (e.g., card networks, bank transfers). Explain key trade-offs and provide a high-level architecture diagram in words.