Can't drop a single leg from a conference call via API

Hey folks, trying to hang up on one participant in an active conference without killing the whole thing. I’m hitting POST /api/v2/telephony/phoenix/conversations/{conversationId}/participants/{participantId}/disconnect but getting a 404 Not Found. The ID looks valid since I pulled it from the GET /conversations list. Am I missing a specific header or is this endpoint busted for conferences?