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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →An idempotency key lets a payment API recognize that a retry belongs to an operation it has already received. If a request times out, reuse the same key with the same request instead of sending a fresh operation: the server can then avoid performing the payment action twice. This protection depends on the provider’s implementation and key-retention policy.
Why a timeout does not tell you whether a payment happened
A client can lose its connection after a server has received and executed a payment request but before the response reaches the client. From the client’s perspective, the outcome is unknown. Sending the request again without deduplication may repeat its side effect. Stripe describes idempotency keys as a way to retry safely after a connection error (Stripe’s explanation of idempotency).
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An idempotency key is a client-generated identifier attached to a request. The API uses it to recognize later attempts as retries of the same logical operation. The IETF HTTPAPI Working Group’s document defines the concept in an Internet-Draft, not a finalized standard (IETF draft on the Idempotency-Key header).
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How to retry a payment request safely
- Create one key for the logical operation. Generate a high-entropy, unique value, such as a UUIDv4. Use a new key for each distinct payment operation.
- Send it with the mutating request. Put the key in the location required by the API provider, such as a request header. Check the provider’s documentation for the exact header or field and which endpoints support idempotency.
- On an uncertain outcome, retry with the exact same key and payload. A timeout or dropped connection is not evidence that the server did nothing. Keep the original key and request data for the retry.
- Use a different key for a different operation. Never reuse a key for a new payment or change the request payload while retrying under the original key.
- Check the provider’s retention window before delayed retries. Once a provider has discarded a key, reusing it may no longer deduplicate the operation.
The IETF draft recommends a UUID or similar random identifier and says a key must not be reused with a different request payload. The draft describes proposed header terminology and syntax; the API provider determines the behavior of its own endpoints.
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What Stripe does with a reused key
Stripe documents that it stores the result of the first request for a key once endpoint execution begins. A later request with that key receives the same status code and response body, including when the first result was a 500 error. This is Stripe’s documented behavior, not a guarantee that all payment APIs behave the same way. See the Stripe idempotent requests reference.
Stripe says it may remove keys after they are at least 24 hours old. If a key has been removed, a later request using it can be treated as a new request. For retries delayed beyond that window, follow the provider’s guidance and first establish the original operation’s status rather than assuming that an old key still protects against duplication.
Stripe also says it does not save an idempotent result when validation fails or when a request conflicts with another request currently executing under the same key, because endpoint execution has not begun. Those requests can be retried. The handling of such cases may differ with another provider.
What to verify in any payment API
Do not assume that one provider’s idempotency behavior applies elsewhere. Before relying on retries, confirm these details in the API’s documentation:
- Where the key belongs: a header, request body, or another field.
- Which endpoints and operations accept keys.
- How simultaneous requests with the same key are handled.
- Whether the API replays stored error responses as well as successful responses.
- What happens if the same key is sent with a different payload.
- How long the provider retains keys, and what it advises for retries after that period.
The available documentation establishes Stripe’s behavior and the IETF draft’s general recommendations; it does not establish the corresponding implementation details for other providers. Check the documentation for the specific API and version you use.
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