CXone v2 Reporting API: Real-time queue stats returning empty JSON

Why does the CXone v2 reporting endpoint for queue stats returns an empty array for real-time data?

GET /api/v2/analytics/queues/realtime?from=now&to=now&groupBy=queue

The request returns 200 OK, but the body is just . I verified the queue ID via /api/v2/queues. This works fine in dev but fails in prod. Am I missing a scope or a parameter?