What specifically is the error? Throughout all the Ventura betas the native L2TP VPN client would break (when previously working) and not allow config through the settings page. The fix is to create a VPN config using Apple Configurator or push a VPN config from a MDM like Meraki SM or another platform.
The Apple Configurator option is pretty easy and the app is free.
When using Meraki-hosted authentication, the VPN account/username setting on client devices (e.g. PC or Mac) is the user email address entered in the dashboard.
The instructions below are tested on Mac OS 10.7.3 (Lion).
Open System Preferences > Network from the Mac applications menu. Click the "+" button to create a new service, select VPN as the interface type, and choose L2TP over IPsec from the pull-down menu.
Server Address: Enter the hostname (e.g. .com) or the active WAN IP(e.g. XXX.XXX.XXX). Hostname is encouraged instead ofactive WAN IP because it is more reliable in cases of WAN failover. Admin can find them in the dashboard under Security appliance > Monitor > Appliance status.
Account Name: Enter the account name of the user (based on AD, RADIUS, or Meraki cloud authentication).
Click Authentication Settings and provide the following information:
User Authentication > Password: User password (based on AD, RADIUS or Meraki cloud authentication).
Machine Authentication > Shared Secret: Enter theshared secret that admin created in Security appliance >Configure > Client VPN settings.
Click OK to go back to the main VPN settings page, then click Advanced and enable the Send all traffic over VPN connection option.
The VPN connectivity will not be established if you don't enable the Send all traffic over VPN connection option.