# Idempotency in HPP

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⏱ 5 min
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👤 Onboarding Developer Team (Alexandre S.)
The core intention behind the Hosted Payment Page is to free the merchant from any troubles about
integrating with Ratepay's payment APIs. One key aspect involved in payment processing is about idempotency
(meaning, what happens if the merchant sends two duplicate requests concerning the same order).

In order to do that, the merchant can opt-in for several different strategies:

1. Ratepay would calculate the idempotency key automatically, based on the supplied payload.
2. Ratepay would calculate it automatically but excluding the buyer ID. This option suits merchants that would reuse buyer ID's or do not supply it at all.
3. Ratepay would calculate it automatically but would exclude shopping baskets.
4. The merchant send a custom idempotency key whenever creating the session, through the `Idempotency-Key` header (as seen in the [API to create sessions](/apis/hpp/openapi/hpp_api/session-management-api/createsession) ).


Notice that the first three strategies are configured directly by your Ratepay representative, but the last strategy has precedence over that - if the idempotency key is supplied, that will always be used and the other strategies would be ignored. This enables the merchant to have complete control about the process.