Why a Successful Screen Does Not Prevent a Duplicate Purchase

When a network connection drops after a customer clicks 'Buy', the server may never confirm whether the order was created, prompting the customer to try again and risk a duplicate charge. The concept of idempotency addresses this by ensuring a repeated request does not repeat its effect on the server. A practical approach separates two identifiers: a quote ID that locks in the offer details, and an idempotency key that tracks whether a specific purchase attempt has already been processed. The server uses a durable record linking the authenticated customer, the operation, and the attempt key to either return the original result or reject a conflicting request. Critically, the browser controls only what it displays, while the server alone must govern what data it creates or modifies.