Bulk update agent skill proficiencies via CXone REST API

Trying to bulk-update agent skill proficiencies using the CXone REST API. The docs show a POST to /api/v2/users/skills, but I’m getting a 400 Bad Request when sending multiple skill assignments in one payload. Here’s the JSON structure I’m using:

[
 {"userId": "123", "skillId": "456", "proficiency": 5}
]

Is there a specific endpoint for bulk operations, or do I need to loop through individual PUT requests? The single update works fine, but performance is killing us with 500+ agents.