Can't connect Client VPN from iOS device

[Kartikai1]

Have Client VPN set up with RADIUS and no problem connecting with Windows client & MAC, but when trying to connect with same credentials on iOS device get error "The L2TP-VPN server did not respond.  Try reconnecting. If the problem continues, verify your settings and contact your Administrator."

We try wit old IPAD (IOS 9.3.5) and newer version of IPhone (IOS 15.2.1) same result.

Fund nothing in meraki log to help

Thanks for any assistance.

[BrandonS]

Bit of a wild guess, but maybe the iOS devices are using ipv6 only?  I don't think client VPN via ipv6 is supported except maybe in the most recent beta releases.