Rublon is hosted on Amazon Web Services (AWS). As a result, Rublon’s IP addresses change from time to time (we have no influence on that).
A firewall may not recognize a new IP address assigned to Rublon, which will cause the firewall to block Rublon. When a firewall blocks Rublon, Rublon 2FA cannot be completed.
Most firewalls use an allowlist. An allowlist is a list of IP addresses that the firewall will never block.
Solution: Use the AWS IP Ranges JSON file and add the IP addresses from the EC2 eu-west-1 region to your firewall's allowlist.
The AWS IP Ranges JSON file contains all current and expected IP addresses that Rublon may use. Rublon’s applications and features that use these IP addresses include but are not limited to: Rublon Authentication Proxy, Rublon Admin Console, Rublon Prompt.
Moreover, add https://core.rublon.net to your firewall’s allowlist.
AWS IP address ranges - AWS Documentation
Rublon Admin Console - Documentation