Yah, the name resolution for the service names can be different, I bet that in your /etc/services file you will see an entry for 8443 to resolve to pcsync-https.
But yes, this is the correct reading, so it’s most likely only a problem with the connection to your server.
The ICE Host Override setting should in such a single-server scenario be set to the domain of your mattermost application server, so if you access your mattermost installation with https://mattermost.mycompany.com, make sure that the ICE Host Override is set to mattermost.mycompany.com and restart the plugin (disable/enable).