# Interview — Payment State Machine & UNKNOWN

**Q: What is the main failure mode?**

A: A timed-out broadcast can be mined even though the HTTP caller saw an exception.

**Q: How do you mitigate it?**

A: Track transaction hash and UNKNOWN state; reconcile with on-chain receipt before settling.

**Q: Is this demo production-ready?**

A: No. It illustrates an invariant in memory; production requires durable storage, retries, monitoring, security, and integration tests.