Post WebGIS DR restore error: Invalid Token for federated server

[WarrenMedernach]

Current environment:

• 2 servers at 10.8.1, both running Windows Server 2016:
  • 1 primary hosting server running Portal, Server and webadaptors
  • 1 image server

I've completed a WebGIS DR restore to a new machine for our primary hosting server, and now when I try to federate the second server (Image Server) it is returning and error when it validates:

Error: The server at 'https://<FQDN of image server>:6443/arcgis/admin/info' returned and error. Server machine 'https://<FQDN of hosting server>:7443/arcgis/sharing/rest/community/self' returned an error. 'Invalid Token'.

Any ideas where to dig into this?