Microsoft 365 Exchange Mailbox API poller - "invalidauthenticationToken"

Hi all, I'm trying to set up the API Mailbox poller for our O365 Mailboxes.

I've followed the somewhat 'scattered' instructions in the Success Center and also received guidance from SW Support but something is still amiss

Once I have selected 'send request' i get the below error:

The request URL is the standard template URL of "">'D7') I've seen somewhere that these  test URL's (/beta) should not be used in prod environments so it could be that

With assistance from our onsite Azure Guru I've set up the OAuth 2.0 authentication, registered the SW app in Azure, configured the API permissions as per SW documentation, setup the secret and then entered all this into API Poller Settings in the template

What am I missing here? (I accept it's most likely something really simple and am pre face-palming in advance)

Many thanks