You likely federated Portal and server using an incorrect admin URL. Do you recall what URL you entered? If you go to the certificate assigned to that URL, does the hostname of the match the CN?
For example, in Chrome through the dev tools and security tab, you can check the CN of the certificate, (Issued to information). I'll assume you don't have any Subject Alternative Names, so the Issued To hostname should match the hostname you used during federation for the admin URL.