Restore a previously archived training identified by its external reference ID (apiId): its ARCHIVED flag is cleared and it becomes active again. Linked courses that were locked when the training was archived stay locked. When several archived trainings share the same external reference ID, the most recently updated one is restored; active trainings are never selected. Restoring when only active trainings carry the reference ID returns 409 Conflict with error code TRAINING_NOT_ARCHIVED; an unknown reference ID returns 404 TRAINING_NOT_FOUND. No webhook is dispatched.