Solved: iPhone and Mac do not connect to Synology L2TP/IPSec VPN: The L2TP-VPN server did not respond

Error message: „The L2TP-VPN server did not respond. Try reconnecting. If the problem continues, verify your settings and contact your Administrator.“

Solution:

Go to Synology and open the VPN server. Open the settings menu for L2TP/IPSec VPN.

Remove the checkmark from “Enable SHA2-256 compatible mode (96 bit)”.