# Idempotency

> Some API endpoints support idempotency, allowing you to safely retry requests without duplicating actions.

Some API endpoints support idempotency, allowing you to safely retry requests without duplicating actions.

To use this feature, include an `X-Idempotency-Key` header in your request. The key must be a unique, UUID-formatted 36-character alphanumeric value.

A request with a new idempotency key will be processed. If you resend the same request with identical credentials and idempotency key, BVNK returns a 400 `Bad Request` status and indicates that a request with this ID already exists. This feature is especially useful for critical operations such as transferring funds, creating payment orders, or updating resources.

:::warning Exceptions
For certain endpoints, a second API call with the same `X-Idempotency-Key` and an identical request body may return `200 OK` with the same `reference`.

For example, this behavior can be observed in the `platform/v1/customers/*` and `platform/v1/customers/agreement/*` endpoints.
:::

For example, if a payment order request times out due to a network issue, you can repeat the call with the same idempotency key to ensure only one payment order is created. Only successful requests are cached. Failed requests are not stored, so you can retry them without risk of conflict.

```curl Idempotent Request
curl --request POST \
     --url https://api.sandbox.bvnk.com/ledger/v1/wallets \
     --header 'X-Idempotency-Key: 1e74002e-74a1-48fd-b707-147c3187a3e1' \
     --header 'accept: application/json' \
     --header 'content-type: application/json' \
     --data '
```

:::info For v.2 endpoints, use `Idempotency-Key` header instead of `X-Idempotency-Key`.

```bash
curl --request POST \
     --url https://api.sandbox.bvnk.com/payment/v2/transfers \
     --header 'Idempotency-Key: 1e74002e-74a1-48fd-b707-147c3187a3e1' \
     --header 'accept: application/json' \
     --header 'content-type: application/json' \
   --data '
```
:::