Unable to add new appliances to existing ZENworks zone

I have an existing ZENworks zone with two version 23.4 primary servers running on Windows. With the deprecation of Windows for primary servers, I'm adding two appliances to the zone.

Initial standup of the appliances went fine and I can login as root. However, when I try to point to either of the existing primary servers to add the appliances, I get the error "Unable to authenticate to primary server." I'm using my personal Super Admin account for the add.

Thoughts?