Trying to sync O365 calendar with Zoom. Not allowed to sign in to O365 via Zoom?... Wha?!?

Hi Zoomers

I am using a MacBook and Safari browsers to do all the following steps (using browser, not apps)

As in Subject line, I am trying to sync my Outlook calendar to Zoom.

I follow the steps correctly.  

At one point in the process I am asked to sign in to my Microsoft account.

(I have my Microsoft365 account opened in the neighbouring tab.  I know how to log in to O365...)

I get an error message that states:

             "(domain name).com isn't in our system. Make sure you typed it correctly."
(Again, I am logged into O365 in a different browser tab.  There is an account under my domain and I can log into it without problems - it is currently opened in the other browser tab!!)

Any ideas why attempting login to O365 when instructed by Zoom to do so will not work?   Even though I can login to O365 when independent of the Zoom instructions about syncing Zoom to Outlook calendar?...

Thanks in advance for explanations / suggestions.

Lesab