CXone /agents/states returns empty array for logged-in agent

Calling GET /api/v2/agents/states and getting a 200 OK with an empty array []. The agent is definitely logged in and active in the UI, but the API isn’t picking it up. Is there a specific capability or filter I’m missing? Here’s the cURL I’m using:

curl -X GET "https://<org>.niceincontact.com/api/v2/agents/states?agentId=12345" \
 -H "Authorization: Bearer <token>"