CXone Reporting API v2: Agent state history query returning empty results

Trying to pull agent state history for the last 24 hours via the CXone Reporting API v2. I’m injecting the standard timeRange and groupBy parameters, but the response is always an empty array. Here’s the query:

GET /api/v2/analytics/reporting/query?timeRange=24h&groupBy=agentId

The endpoint works for other metrics, but state history seems to ignore the time filter. Am I missing a required header or is the groupBy syntax wrong for this specific metric?