Idempotency explained — Part 1: basics, idempotency key and Go implementation

The user clicks "Pay". Nothing happens. The network is slow, the spinner keeps spinning. They click again. This time it goes through. Your API received two identical requests 800ms apart. Two possible scenarios. Either your customer just got charged twice — and you have a legal problem, a chargeback to handle, and a difficult conversation ahead. Or you thought about idempotency, and the second request is treated as a duplicate: same response, zero additional side effects. What is idempotency? Th