So
hall.com has some signup funniness. It automatically puts you into a 'network' of other people from your same domain, so if you use a
gmail.com email address you will have a
gmail.com 'network' on the left of their site, with strangers :/
You should also see an 'out of network rooms' section on the left with the 1GAM room in it. This is the important bit. If you don't have that after using the invite link please email me and i'll invite you directly to the room.
Shame it's not more straightforward to join, but it IS a very nice chatroom once you are in!