In financial systems, executing the same request twice (like a payment) can be catastrophic. A user might: Get charged twice See double entries Or even worse, lose trust in your system To avoid this, APIs (especially for payments) often support idempotency keys . But not all backends or platforms provide built-in support. So I built one from scratch for my Kotlin backend. 🔁 What is Idempotency? In software engineering, idempotency means that performing the same operation multiple times produces the same result as doing it once. In simpler terms: If you submit the same request twice, only one result should be processed. 💡 Real-world analogy Imagine clicking a “Pay Now” button. You click once — nothing happens — so you click again. Without idempotency, you might be charged twice . With idempotency, only one charge goes through — even if the button was clicked multiple times. 🛠️ In APIs Many APIs (especially payment gateways) accept an idempotency key , the...