⚠️ 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 report without changing the report, its constituent reimbursement records, timestamps or generated output. This action requires permission to view the reimbursement report and the ReimbursementReports.update-custom-fields permission.

The customFields object accepts Boolean, Text, Long text, Email, URL, Number, Date, Date-time and JSON values according to each administrator-defined field. It may be empty. Omitted identifiers remain unchanged, while an explicit null clears the corresponding value. Every submitted identifier is validated against the report's current operator owner, the current custom field configuration and the acting administrator's access. Unknown, inapplicable or currently disabled identifiers return a 422 error keyed as customFields.<identifier>, and no submitted values are changed.

This write action does not accept query parameters or includes. The response is the current default read representation after applying the values, including the report's prepared monetary aggregates; customFields remains live metadata and is not a point-in-time snapshot.