The Team Drive has been renamed into Shared Drive. This comes with some changes in the level of user access which affects reviewers.
If the Google Sheet is saved in a Shared Drive, please make sure reviewers are granted "Manager" level of access on the shared drive, as shown:
The following error message appears when a reviewer with no Manager level of access is added:
“You do not have permissions to access the requested document. Email address cannot be added”
Doing the above steps makes sure the reviewer email address can be set via the add-on. This is a current limitation set on Google's end and beyond our control.