⚠️ Experimental endpoint — not yet a stable contract. This action ships as experimental / beta. While experimental, its schema and behaviour may change without a version bump — including breaking changes within v1.0 itself. Anyone consuming it does so for evaluation only, or by coordinating adoption with their account manager so changes can be sequenced with them. It graduates to a stable, version-locked contract (where the normal breaking-change rules apply) only when this experimental notice is removed.

Set the applicable live custom field values of a reimbursement record without changing its immutable financial, policy, tag, calculation, or timestamp data. This action requires permission to view the reimbursement record and the ReimbursementRecords.update-custom-fields permission.

Send a JSON object containing only the required customFields object. Additional body properties and query parameters return 422 validation errors. Omitted identifiers remain unchanged, while null clears the corresponding value. When custom fields are enabled for reimbursement records, an empty object succeeds as a no-op. Invalid or unavailable identifiers and invalid values return 422 validation errors, and no submitted values are changed. If custom fields are disabled for the tenant or reimbursement records, the action returns 412 Precondition Failed. Neither rejection changes submitted values.

A 404 response means the reimbursement record was not found.