PATCH /conversations/voice/participants transfer action returning 400 Bad Request

Trying to transfer an active voice call to a different queue via the Conversations API. I’m sending a PATCH to /api/v2/conversations/voice/participants/{participantId} with the transfer action and target queue ID in the to object. The request consistently returns a 400 Bad Request with invalid_transfer_target error. I’ve double checked the queue ID exists and is routable. Here’s the payload I’m using:

{
 "action": "transfer",
 "to": {
 "id": "queue-uuid-here",
 "type": "queue"
 }
}

Am I missing a required field or is there a specific permission needed on the OAuth token for this action?