I started by outlining a high-level architecture for the checkout flow. Mentioned main components like the cart management system, payment gateway, and order fulfillment.

The interviewer seemed intrigued and asked about how I would handle high traffic. Discussed strategies like caching, horizontal scaling, and database sharding.

Then, I moved on to security concerns such as PCI compliance for payment processing, which impressed the interviewer. However, I stumbled a bit when asked about error handling—ran out of time to fully articulate a solid plan.

The interview ended on a positive note, but I left with a nagging feeling about the incomplete parts.