Every payment flow has a silent enemy: the network. Requests time out, connections drop, users panic, and click twice. What happens to your system when the same charge arrives more than once? I used to think idempotency keys were one of those "nice-to-have backend things." You know the kind you tell yourself you'll fix later. That thinking is dangerous. When it comes to payments, idempotency isn't a feature; it's what prevents duplicate charges and inconsistent state. The Problem: "The Double Tap" Imagine this: A user clicks "Pay" The network is slow, or their Wi-Fi drops They click "Pay" again Your API receives two identical requests If you're not handling this correctly: The user gets charged twice Your database ends up in a weird state You lose user trust instantly This doesn't require a bug. It's normal behavior in distributed systems. What Is Idempotency? In simple terms: You can send the same request multiple times, but it will be processed only once.…