Why is my Android mobile device not connecting to the QuickVPN server on my AQUILA PRO AI router?

The QuickVPN server on AQUILA PRO AI devices uses the Certificate Authority (CA) with a 2048-bit RSA key size, which is currently the latest and most recommended choice since the 1024-bit RSA keys are no longer considered secure and not in use on the QuickVPN server. For security purposes, we have restricted the use of certificates with RSA lower than 2048bit. Android mobile devices currently will not be able to connect to QuickVPN server without RSA 2048-bit RSA key.

As Android 11 or earlier are not yet compatible with 2048-bit CA as of today, and Android 12 removed the L2TP over IPSec option in VPN types, which is a necessary tunneling protocol, you cannot connect to the QuickVPN server with your Android devices.