⚠️ 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 custom field values of a session without changing any other session properties. This action requires permission to view the session and the Sessions.update-custom-fields permission.

When custom fields are enabled for sessions, the customFields object may be empty; an empty object succeeds as a no-op without creating a value audit. Omitted identifiers remain unchanged, while an explicit null clears the corresponding value. If custom fields are disabled for the tenant or for sessions, an empty object returns a 422 error keyed as customFields, while a populated object returns errors keyed as customFields.<identifier>. Every submitted identifier is validated against the session, the current custom field configuration and the acting administrator's access. Unknown or inapplicable identifiers also return a 422 error keyed as customFields.<identifier>, and no submitted values are changed.