Synchrony needs to run on a port that is different from Confluence. If Confluence is using 443, then you can not use 443 for Synchrony.
If you look at https://confluence.atlassian.com/confeap/administering-collaborative-editing-847355676.html you will see a section at the bottom about changing the port. It says:
Synchrony runs on port 8091 by default. If this port is already in use by another application on your server you can use the the synchrony.port system property to change it to an available port.
If you're Confluence 6.0.3 or earlier you'll need to use reza.port instead of synchrony.port.
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