Help with setting up Gmail Android app client please

I raised this problem (text below) as a ticket 5 days ago, with no response! Can anyone help please?

"Several weeks ago something changed (the app, I think) and the app is now almost useless. I can't see my 2 inboxes on my phone.
In contrast, on my Chromebook, I use web-based Gmail to handle both accounts, and that still works fine."

One account is my @gmail.com one and the other is one hosted by Inmotion.

The Help documents I have looked at here seem rather out of date!