I have the same problem on AEM 6.3. Cannot publish (activate) pages from 6.3 Author server to 6.3 Publish server.
It works on 6.2 (previous version) but it does not work on 6.3 (newest version).
No information in the documentation.
I see no issue in Replication on Vanila AEM 6.3 instance.. Have you ensured that the replication agent is configured properly. By default it is pointed to 4503.. So if you are running publish on a separate port, you need to change it in the replication agent setting
Could you check that port 4502 and 4503 is block or using by some other application.
Check your AEM Configuration Apache Felix Jetty Based Http Service. in this check http port in Both AEM Instance.If they are pointing to same port.Change one of the Port.