Hi @marius.stanasel, welcome to the Cayenne Community. (and @osinno if you're still out there this may be of some interest to you as well)
For a few months now, the UI for adding an Actility device has allowed you to enter a custom server, so you're no longer limited to the list in our dropdown menu, just start typing in the field. I should note that what our server is looking for here is called your ThingPark DX Profile, which is generally your domain with -api appended, without the .thingpark.com part.
So if the server you were looking for was, for example, example.thingpark.com, what you should enter in this field is simply example-api. Give it a try for your KPN server and let me know if you have any trouble.