> ## Documentation Index
> Fetch the complete documentation index at: https://loyalty-interchange.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Idempotency and duplicate delivery

> Choose stable business keys for loyalty mutations, transport retries, offline queues, and webhooks.

A client can lose the response after the server commits. Every financial
mutation therefore needs a stable operation-scoped key derived from its source
event:

```text theme={null}
evaluate:order-123
accrual:order-123
reserve:order-123:redemption-7
capture:order-123:reservation-7
adjustment:order-123:refund-2
```

An identical replay returns the original outcome. The same key with changed
business data returns `409 idempotency_conflict`. A transport retry may use a
new request id and timestamp, but retains the business key. Never retry a
mutation with a new random key.

Offline queues persist source event id, operation, payload fingerprint, and
delivery status. Webhook consumers verify the signature, deduplicate delivery,
then reconcile the resource. Test initial request, exact replay, and conflicting
replay for every mutation.