Hey beerarman,
I've got the same problem from 2 Echo Shows I bought over Christmas, they've been tried with 2 established accounts, 2 internet connections and over two devices.
However, I've recently created a brand new Amazon account, factory reset the Show and logged into both the Echo and the Alexa app with the new details. This looks to have work OK and the Echo Show is now online within the app (I can also link Spotify to it).
So, it looks like the problem is to do with an Amazon account - sadly it doesn't look like it's a common issue and when I called support they told me one person has complained about it and it's being "looked into". I'm going to ask Amazon to merge my two accounts if possible to see if that works.
Might be worth giving a shot for you too.
James