Refund Session

Process a refund for a session. Only `approved` and `partial_refund` sessions can be refunded; any other status returns `400` (`Only approved or partially approved sessions can be refunded.`). A `200` with `Session refunded successfully` means the refund was submitted, not that the money has moved, and the response body shows the session as it was before the refund changed its status. Follow the session status, `refund_processing` and then `partial_refund` or `refunded`, and the `refund_processing`, `refund_claimed`, and `refund_failure` webhooks. **Auth: Payments capability bearer token** (the site credential JWT or Gateway merchant auth token). The Checkout merchant token you use to create sessions is rejected with `401` (`Invalid token or expired token`). The session must belong to the token's site.

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