I understand. I can only tell you the following about this:
Federation can be tricky, and an incorrect entered URL can keep servers from property communicating. To view federated ArcGIS Server information in Portal Admin, go to Federation | <serverID>. You will see something like the following screenshot.
The two parameters of interest here are url and Admin Url should be the FQDN URL to/arcgis and Admin Url should be internal machine name over port 6443 to /arcgis. Ensure that these are correct; if they are not, you will need to unfederate (via the Unfederate Support Operation) and federated again. Note that re-federating will require changing ownership back to the publisher account, as re-federated services will be owned by the administrator that performed the federation.
You can also review the Portal logs.
I hope to help you with this post.
Ref.: Mastering ArcGIS Enterprise Administration (Chad Cooper)