Issue adding Office365 mailbox

I’m having trouble adding a client’s Office 365 mailbox to the eM Client.
Any idea what the issue may be?

p.s. I have added different client’s Office365 mailboxes before and they work.

If you are using the automatic email wizard and getting that error, from Googling Microsoft forums they say it can be something to do with your “Subscription environment” and is not getting the correct Office365 OAuth token when you allow eM Client access to your account.

Also might be also related to your eM Client version. What version are you running ? and do you have Windows or Mac.

The only other thing I can suggest is try and clear your browser cache and cookies etc and try again. Might just be a local browser issue with an old or outdated token. Just a thought to try.