Hi @chris661, welcome back, and sorry you're having trouble changing over to Norton.
That would mean you would need to be on either of these versions which should be ok i believe:
OS 10.15: Catalina - 2019
OS 11: Big Sur - 2020
OS 12: Monterey - 2021
The server error usually indicates that you're not using the BTID or have not claimed the Account Holder Status on the BTID. Please check this and post back to let us know how you get on.
In case this was the error, I changed my password for My BT account, and it worked !
I now have Norton installed