Unable to configure L2TPoverIPsec connection.

Nemesis

Hello.
Unable to configure L2TPoverIPsec connection. I use: OS Ubuntu server CLI only (no GUI), Zyxel Zywall USG 110.
The tunnel has been tested on other OS Win10/Ubuntu mate 20.04 everything works fine.
Now I need to set up a connection using xl2tpd/strongswan.
The methods and instructions for connecting through the network manager are done through the GUI.
To test my connection, I use a VM, a "clean" ubuntu server 20.04.Then I installed xl2tpd,strongswan.
The Zyxel tunnel is now configured with PES=DH-2, Related Settings=none, following the advice of Zyxel technical support. Ubuntu server picks up strongswan but doesn't pick up xl2tpd. The ppp0 interface does not appear. After making changes to the parameters: PES=DH-2, Related Settings=none, connection via Win10/Ubuntu mate 20.04 fails.
I contacted those Zyxel support, they tested their tunnel with a connection via xl2tpd / strongswan, everything connects to them. They couldn't help me with my setup.
 P.s. In my project, a server with a database is used, the GUI will not pull out. Please help me solve this problem.

CHS

You can refer to askubuntu forum thread. (https://askubuntu.com/questions/1335338 )
There is someone suggest to use network-manager-l2tp for L2TP connectrion.