YouTube Live Streaming API (Restricting LiveChat participants)

Hi all, have a feeling this might not be the best sub -- but haven't found a closer one. Gentle shove in the right direction is appreciated if I'm really off the mark here. TIA!

I am implementing something to handle a full YouTube Live Stream life cycle completely via automation (managed via other automation). Everything (creating, starting, binding, posting Live Chat messages, ending, finalizing, updating) is working really well, except...

I'd like to restrict posts to the Live Chat to specific users. In the YouTube Studio GUI this is referred to as "Live Commentary (Approved Users)"

So far as I can find in the YT API docs (https://developers.google.com/youtube/v3/live/docs and https://developers.google.com/youtube/v3/docs/ specifically) this doesn't seem to be possible -- but given how much else can be done I feel like it "must" be there and I'm just missing it or its called/documented in a way that isn't obvious to me.

It would be awesome if this could be set on a channel level as a default, but even if I have to call "some API" as part of the live stream creation portion every time that would be awesome. Ideas?

(In theory I could just clean up the Live Chat after the fact by deleting messages but that seems like a very backwards approach not to mention being very API-quota-intensive)

Again apologies if I'm in the wrong place and thanks in advance!