Channel Invites not working

I'm trying to get a user onto a beta release channel but it's not working. I've had success adding other users, just not this one. I've done both email invite and URL link and neither work. The user doesn't see anything in the headset or on the horizon app in the store.

I've also had them go to the store in the headset, search for the app name, but it's not showing up. This was a workaround in the past for the app lab at least.

Anyone have any suggestions??