Setting up a second Microsoft Exchange Account in Microsoft Outlook Desktop

I'm currently working on two projects and am having problems having both email accounts (Office 365; Exchange) on a single Microsoft Outlook Desktop windows client. I had done it before (quite easily) and it was working for months, and then the second account stopped connecting (was stuck on 'trying to connect'). So I removed the second account and tried to connect to it again. I go through all the 'Add Account' steps, including logging into the account successfully and validating via SMS code. Then the wizard churns for ages only to fail i.e. with a window saying "Something went wrong and Outlook couldn't set up your account. Please try again etc, etc." I've tried several times, always with the same result. I've done some searching but have not yet found a working solution. Can anyone advise and/or asist?