Doc for WWM states that a filter when using a firewall is necessary. Any ideas about which port etc?
Thanks

Where does it say that?

In the help file of the app.
FireWalls
If you use a fire wall, you must create a filter for this application to communicate with the webserver. Otherwise your firewall will block the app from communicating with the server, and return an "Alert" message even if your server is working properly.

That just means you need to open port 80 to the application.