Cisco Secure Client / AnyConnect - No connection to VPN service. Reattach failed. - Connect capability is unavailable because the VPN service is unavailable.

On macOS 14 Sonoma, Cisco Secure Client / Cisco AnyConnect does not appear to install properly. This affects updates as well as new installations.

The topic was previously discussed in cisco Secure Client Macos, service is una… - Apple Community, but I'm unable to respond there, since Apple thinks contributing to a conversation in which nobody has engaged for a while is not something people should be able to do. Therefore, I had to start a new discussion here.

The following error message appears when starting the client:

When attempting to connect, the following message appears:

Several other forum posts discussed this issue and suggested that the respective .plist file be added manually to launchctl, however, the file did not exist on my system even with a clean installation. Thanks to Joel W. from Arizona State University's tech support, I was able to resolve this issue after having spent 3 hours on it.

The .plist file is part of the package contents of the "Cisco Secure Client - AnyConnect VPN Service" app. It can be extracted from there, copied into its appropriate place in the Library folder, and added to launchctl with the following two commands on the Terminal:

sudo cp /opt/cisco/secureclient/bin/Cisco\ Secure\ Client\ -\ AnyConnect\ VPN\ Service.app/Contents/Resources/com.cisco.secureclient.vpnagentd.plist /Library/LaunchDaemons/
 
sudo launchctl bootstrap system /Library/LaunchDaemons/com.cisco.secureclient.vpnagentd.plist

After a restart of the Cisco Secure Client, everything worked as intended. Thank you, Joel W.!