Preventing Double Charges: Why API Idempotency Matters

Idempotency is critical for financial APIs and distributed systems where network failures or user retries can cause duplicate processing. Without idempotent design, a single payment can be charged multiple times, a message delivered twice, or an order created duplicate—each with serious business consequences. Understanding HTTP idempotency semantics and implementing idempotency keys is essential for building reliable payment systems and handling at-least-once delivery guarantees.