API Idempotency: Best Practices for Reliable Payment Processing

Idempotency ensures that a request can be safely retried without causing unintended side effects. In payment processing, this is critical — you never want to charge a customer twice because of a network timeout.

How It Works

Clients generate a unique idempotency key for each request and include it in the Idempotency-Key header. If the same key is used again within a certain time window, the API returns the original response instead of processing a new request.

Implementation

At KmarApp, we store idempotency keys in the database along with the response. When a duplicate request arrives, we return the cached response. Keys expire after 24 hours.