The CTO Podcast with Fexingo · 2026-08-31 · 11 min
In this episode, Lucas and Luna dig into a deceptively simple engineering decision that has quietly shaped the reliability of modern fintech: idempotency keys. Using Stripe's payout API as the central case, they unpack how a single HTTP header prevents duplicate charges, double refunds, and the kind of cascading failures that keep payments engineers up at night. They trace the pattern from Stripe's early days to its use in everything from Square's terminal SDKs to open-source projects like Idempotency-Key, and they explain why the concept is now a baseline expectation for any API handling money. Along the way, they touch on the trade-offs of distributed systems, the psychology of 'at-least-once' delivery, and why idempotency is as much a product decision as it is a technical one. If you've ever wondered how payments companies sleep at night, this episode gives you the answer: carefully, with idempotency keys in place.
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