Conversations API: 400 error when dropping specific participant from conference

Trying to kick a single user out of a conference using the patch endpoint /api/v2/conversations/conferences/{conversationId}. Sending this payload:

{
 "participants": [{
 "id": "participant-uuid",
 "state": "disconnected"
 }]
}

Getting a 400 Bad Request. The docs say state is valid but it’s rejecting the request. Am I missing a required field or is this endpoint read-only?