I've been conducting some experiments and quite frankly the only conclusion available is not good, not good at all.
So just to set the parameters here, there is nothing wrong with the headset, the microphone works fine in other worlds and apps and I can hear other people speaking, they can hear me. There is nothing wrong with audio settings.
Now enter a SECOND headset, brand spanking new, just got from the store today. We setup a brand new account for it and Horizon Central works perfectly, we can hear others and they can hear us. Absolutely no problem.
BUT!! Factory reset the other headset and login with the same account.
Remember both of these headsets have been setup IDENTICALLY, same account, all the settings for both headsets will be the same, same internet connection, everything should be identical, but, on one headset we cannot hear what other players are saying, but on the other headset we can.
There is only one possible conclusion.
META HAS DELIBERATLY BLOCKED AUDIO IN HORIZON CENTRAL FOR THAT HEADSET.
Each headset has a unique ID so they absolutely have the ability to do this, and it is the only explanation that fits.
This is particularly scummy, now I have no choice but to sell the headset and get a new one, the unfortunate person who buys it is going to inherit the problem through no fault of their own. Nice one Meta.
Also it should be noted that Horizon Central has been completely removed from all listings. You can't even find it with a search. The only two references to it that remain seem to be the fixed portal you have in your personal loft area, or the entry in your library on the phone app but contrary to the fake information supplied by dannyk13 up there, ther eis no "Chat" icon in the upper left when you open it, I have no idea why he would give out totally inaccurate information like this. However, while the Horzion Central world appears in the phone app library, it DOES NOT appear on the headset library. Very strange indeed, Meta is doing something decidedly sketchy here. Maybe it's got to do with kids who are far too young being in there, running around shouting "6 7" everywhere constantly, using bad and offensive language, clearly having no parental supervision.