CXone Admin API bulk skill update via PUT /api/v2/users returns 422

Trying to bulk-update agent skill proficiencies using the CXone Admin API. The docs state: “To update user skills, send a PUT request to /api/v2/users/{userId} with the skills array.”

I’m sending this payload:

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

But the API returns a 422 Unprocessable Entity. The response body is empty. Is there a specific format for the skills array I’m missing?