How was idempotency ensured during retry requests to payment gateways?

Idempotency in repeated requests to payment gateways is ensured by using unique transaction identifiers (for example, an idempotency key). When a request is resent with the same identifier, the gateway recognizes it as a repeat and does not create a duplicate payment, but returns the result of the previous operation.

Example:

• The client generates a unique idempotency key for each payment attempt.
• When sending a request to the gateway, this key is included in the headers or body.
• If the request is repeated due to a timeout or error, the same key is used again.
• The gateway checks the key and, if an operation with such a key has already been completed, it returns the saved result without deducting funds again.

This allows requests to be safely repeated without the risk of double charging.