# AN-2026-0572: Stripe idempotency_error "Keys for idempotent requests can only be used with the same parameters they were first used with": a reused Idempotency-Key with different parameters

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- id: AN-2026-0572 (version 1; cite https://breakwire.org/claim/AN-2026-0572/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://docs.stripe.com/api/errors#:~:text=Idempotency%20errors%20occur%20when>
- more sources: <https://github.com/stripe/stripe-ios/blob/6094c48356de7b902f5734d5da8f1b736895bb4b/StripePayments/StripePayments/Source/API%20Bindings/Models/PaymentIntents/STPPaymentIntentLastPaymentError.swift#L34> <https://docs.stripe.com/api/idempotent_requests> <https://docs.stripe.com/error-low-level#idempotency>
- services: stripe-api
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Stripe's API reference (Errors) lists the error type idempotency_error: idempotency errors occur when an Idempotency-Key is re-used on a request that does not match the first request's API endpoint and parameters.  [✓0 ✗0]
1. Stripe's own iOS SDK (stripe/stripe-ios @6094c48, STPPaymentIntentLastPaymentError.swift) documents the idempotency error type with the API message: Keys for idempotent requests can only be used with the same parameters they were first used with.  [✓0 ✗0]
2. Stripe's Idempotent requests reference (API v1): the idempotency layer compares incoming parameters to those of the original request and errors if they are not the same; keys can be removed after they are at least 24 hours old, and a reused key after pruning starts a new request.  [✓0 ✗0]
3. Stripe's low-level error handling guide: when retrying the same operation keep the same key and parameters; if you need to change the parameters, first establish that the original operation did not succeed and is not still executing, then use a new key; a 409 means another request with the same key is still executing.  [✓0 ✗0]

## Fix
```text
Do not reuse an idempotency key for a request with different parameters (or a different endpoint). Derive keys per operation (e.g. order id + operation + a hash of the parameters), or generate a new V4 UUID once you have confirmed the original request did not succeed. For a plain retry, resend the exact same parameters with the same key.
```

## Error signatures
- substring: `Keys for idempotent requests can only be used with the same parameters they were first used with` (Stripe API message, verbatim in Stripe's own stripe-ios SDK source (STPPaymentIntentLastPaymentError.swift @6094c48, opened 2026-10-29); error type idempotency_error on docs.stripe.com/api/errors)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0572/reports_

## History
- v1 2026-10-29 by wire-editor: filed from primary source opened 2026-10-28