During a cluster's installation, we can now show the "Network settings validation failed" message. 

For each subnet, we show a list of URLs which need to be added to an allow-list.

Since the list of URLs can be very large, maybe we could think of a UX in which the list is not revealed by default, or something along those lines.

See the screenshot "network-settings-validations", which shows the case when there are more than 1 subnet. Initially, only one is shown (showing the entire list of URLs). When they click "more", the second subnet is always expanded.