One of the key questions I was asked was to design a payment system from an API perspective. I found this to be the most relevant and engaging part of the process, as it aligned closely with my experience in backend development and API design. I approached the problem by clearly outlining the core components of a payment system, including payment initiation, authentication, transaction processing, and webhook handling for asynchronous updates. I then walked through the design of RESTful API endpoints to support various use cases such as initiating payments, retrieving payment statuses, handling retries, and securely storing payment methods with tokenization. I also addressed considerations like idempotency, error handling, and PCI compliance. The interviewers acknowledged the level of detail and clarity in my approach, and I believe I demonstrated both my technical proficiency and my ability to think through real-world architecture challenges.