Don’t Charge Your Users Twice: Understanding Idempotency

If you’ve ever been in a situation where you paid for pizza online, mustered the courage to begin and complete that transaction and accidentally said “you too” in response to “enjoy your meal. It’ll soon arrive” then you know that the only thing worse than the embarrassment from that conversation is realising that the pizza you ordered for say, $20 (great economy) has ensured you get charged $40 or worse $60. You know what’s worse than that still? Now you have to call the same person and complai