POST /api/v2/conversations/calls 400 Bad Request on behalf of agent

NICE CXone API & Integrations
1

Trying to kick off an outbound call for an agent using the API. The docs say I need to pass the agent’s user ID in the from object, but I keep hitting a 400. Here’s the payload I’m sending:

{
 "from": { "id": "agent-user-id", "name": "Test Agent" },
 "to": [{ "phoneNumber": "+491234567890" }],
 "wrapUpCode": "completed"
}

The error just says “Invalid request” without specifics. Do I need to set the mediaType explicitly to voice? Or is there a permission issue I’m missing?