To access via GMail, one will get 

This app is blocked

This app tried to access sensitive info in your Google Account. To keep your account safe, Google blocked this access

To remedy this, or start on Gmail from scratch, (see other article for Google Workspace account, this is only for @gmail.com) 

Make an app password. 

https://myaccount.google.com/apppasswords

Add account 'Other' to your Email Archiver Pro