We use 365 for Pro Plus.
I logged into the 365 portal using my 365 account and I am able to download 365 Pro Plus - so clearly Azure AD is happy with my account etc.
When Pro Plus is installed, if I "sign out" and open Word or Excel, in the top right it says "Sign in to get the most out of Office".
If I click that I see a "Sign in" windows with a "Microsoft Account Whats This?" and a "Password" box.
If I enter my Office 365 credentials (the ones I used to login and download Pro Plus with) it says "That Microsoft account doesn't exist. Enter a different email address or get a new account".
What is going on?!
I have a ticket open and support have some logs but seem to have never seen this before - I have just build a fresh test VM with nothing other than Windows 7 ISO and I can replicate the issue