At any point in time, FNO-Cloud (EU) might be trying to reach any of 3 public Availability Zones (AZs) hosted by Amazon (and noted below via nslookup).
Here is Amazon's documentation listing the Public IP range for a given region, which might help in terms of whitelisting.
The region used by Revenera cloud services is eu-west-1.
DESITE will, by default, use the system proxy settings. Since version 2.6.4, you can also use manual settings. You can access them by showing the "Extended Options" in the license dialog and then clicking "Proxy Settings."
Apart from the default setting, which is using the global Windows configuration, you can also explicitly forbid the use of a proxy, or explicitly configure a proxy, which can optionally include credentials in case your proxy requires authentication.