CXone Admin API: Bulk updating agent skills via /api/v2/users

Trying to bulk-update agent skill proficiencies via the CXone Admin API. The docs for PATCH /api/v2/users/{userId} show a skills array, but when I send the payload below for a batch of users, it returns a 400 Bad Request. It seems to reject the nested object structure. Am I missing a specific field or is this endpoint just not meant for bulk skill changes?

{
 "skills": [
 { "id": "skill-123", "proficiency": 5 }
 ]
}

The error payload just says “Invalid skill configuration” with no details.