What is idempotency and when is it important? Provide a business scenario.

Idempotency is a property of an operation where multiple executions of the operation produce the same result as a single execution.

This is important in systems where requests may be repeated due to failures, timeouts, or retries, to avoid undesirable side effects (for example, double charging money).

Business Scenario:

In a payment system, when paying for an order, a customer may click the pay button multiple times due to a slow network. If the debit operation is not idempotent, the customer could be charged multiple times. To prevent this, the operation should be idempotent — for example, by checking a unique transaction ID to see if it has already been completed, and not to repeat the debit.

Thus, idempotency ensures reliability and correctness of business processes during repeated requests.