PATCH /conversations/calls/{id} transfer to queue returning 400

Trying to transfer an active call to a different queue via PATCH /api/v2/conversations/calls/{id}. The JSON payload looks right:

{"actions": [{"type": "transfer", "to": {"type": "queue", "id": "queue-uuid"}}]}

But the API keeps throwing a 400 Bad Request with "message": "Invalid transfer target". We’ve verified the queue ID exists and the user has permissions. Is there a specific header or nested object structure required for queue transfers that the docs missed?