# `idempotency_key_reused`

**Status 422.** This Idempotency-Key was already used for a different request.

## What it means

This `Idempotency-Key` was already used for a different request. For 24 hours any different request with it is refused. After that, a points change's key still refuses another member or another amount, because the key is also the change's id in the ledger; the same member and amount is answered as the first change again, whatever the `reason`, and nothing new is made.

## What to do

For a new change, use a new key. To retry the first request, send exactly the first request again.

## Safe to send again?

Not as it is. Change what the answer points to, then send the request.

## What else the answer carries

- `param`: The field, header or query parameter at fault, when there is exactly one.

## Where you can meet it

- [`POST /stores/{store_key}/programme`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#updateProgramme): Change the earn rate, the bonuses, what a point is worth, referrals, spending any amount, the time zone, the ways to earn, or when points expire
- [`POST /stores/{store_key}/programme/rewards`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#addReward): Add a reward shoppers can spend points on
- [`POST /stores/{store_key}/programme/rewards/{reward_id}`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#changeReward): Change a reward's cost, value, minimum order or label
- [`POST /stores/{store_key}/programme/rewards/{reward_id}/remove`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#removeReward): Remove a reward
- [`POST /stores/{store_key}/programme/offers`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#addOffer): Add an offer: a campaign, a product offer or a channel offer
- [`POST /stores/{store_key}/programme/offers/{offer_id}`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#changeOffer): Change an offer
- [`POST /stores/{store_key}/programme/offers/{offer_id}/remove`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#removeOffer): Remove an offer
- [`POST /stores/{store_key}/design`](https://matrixrewards.co.uk/docs/api/2026-10/stores.md#updateDesign): Change the design: colours, words, the panel and product-line look, the account page layout, the terms link
- [`POST /members/{member_key}/adjustments`](https://matrixrewards.co.uk/docs/api/2026-10/members.md#adjustMemberPoints): Add points to a member's balance, or take them away
- [`POST /members/{member_key}/codes/void`](https://matrixrewards.co.uk/docs/api/2026-10/members.md#cancelMemberCode): Cancel a reward code and give the member back its points

Every code, and the shape of an error answer: [Errors](https://matrixrewards.co.uk/docs/errors.md).

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Page: https://matrixrewards.co.uk/docs/errors/idempotency_key_reused
Contract: 2026-10 sha256:35af153960028890fea5738799f5a71e535e1eea4dd3f6b8d5f50b37f02363da