Xfinity Voice - Can't use Advanced Call Forwarding

I am logged into Xfinity Voice using the primary account, but the Advanced Call Forwarding area only ever displays an error message "Sorry, but something went wrong. Please try again in a few minutes." Because Advanced Call Forwarding is inaccessible, I am unable to complete the nomorobo setup per the official Xfinity instructions (Stop unsolicited robocalls to your home - Xfinity Support). I'm getting too many spam calls and adding numbers to the block list is futile.

Please fix my Advanced Call Forwarding.