POST /api/v2/conversations/calls returns 400 Invalid Parameter

Hitting a wall trying to kick off an outbound call from our supervisor dashboard. The API doc says initiator needs an id and type, but I’m getting a 400 with invalid_parameter: initiator.

{
 "initiator": { "id": "agent-uuid-here", "type": "user" },
 "to": [{ "phoneNumber": "+49123456789", "phoneType": "work" }],
 "from": { "phoneNumber": "+49987654321", "phoneType": "work" },
 "wrapUpCode": "outbound"
}

The token has conversation:call:write. Am I missing a required field or is the type value wrong?