In addition, I just installed apex, granted access to the acl, but apex returns the same error.
I did not run the epg config, this was the issue for Apex.
I tricked myself here.
I set the https post to 5500 on CDB and 5520 to PDB.
Then I wanted to access the CDB on the 5520 port, and that threw the error.
So if you configured a PDB https to a deifferent port, you can't access the CDB from there, but just the PDB, and vice verse.