After installing

Testing that the server works

ManicTime Server is now up an running. If you open a browser on the machine where it is installed and go to (port might differ)

http://localhost:8080

you should see the server's login screen.

Firewalls and routers

Now make sure that it is visible to other machines. On some other device, open a browser and try to go to the server. You will probably have to write an IP of the server's machine

http://<some ip>:8080

If this does not work, then ManicTime client also won't work. Usually the problem is firewall or router. If you have a firewall, make sure that it allows connections to the server. Same thing if you have a router. You need to allow incoming connections (port forwarding) to the server.
Before you try to connect in ManicTime, always first try to make the connection from a browser.