Can not connect to ikev2 vpn from Ubuntu 22.04

I created ikev2 server with strongswan. And trying to connect to it from Ubuntu. When I connect from Android it works, so there is no problem with server, there is problem with client.

What I've done from client side on Ubuntu:
installed strongswan

sudo systemctl start strongswan-starter

installed necessary plugins:

sudo apt install strongswan libcharon-extra-plugins

Coppied CA certificate to path:

sudo cp /tmp/ca-cert.pem /etc/ipsec.d/cacerts

Put credentials to secrets:

sudo nano /etc/ipsec.secrets

username : EAP "password"

Created config file:

sudo nano /etc/ipsec.conf

config setup

conn ikev2-rw
    right=server_IP
    # This should match the `leftid` value on your server's configuration
    rightid=server_IP
    rightsubnet=0.0.0.0/0
    rightauth=pubkey
    leftsourceip=%config
    leftid=username
    leftauth=eap-mschapv2
    eap_identity=%identity
    auto=start

And finnaly started the strongswan:

sudo systemctl start strongswan-starter 

When I check ipsec status, there is no errors:

systemctl status ipsec

strongswan-starter.service - strongSwan IPsec IKEv1/IKEv2 daemon using ipsec.conf
     Loaded: loaded (/lib/systemd/system/strongswan-starter.service; disabled; vendor preset: enabled)
     Active: active (running) since Sat 2023-06-03 13:44:37 KIV; 1min 49s ago
   Main PID: 11633 (starter)
      Tasks: 18 (limit: 37659)
     Memory: 7.9M
        CPU: 29ms
     CGroup: /system.slice/strongswan-starter.service
             ├─11633 /usr/lib/ipsec/starter --daemon charon --nofork
             └─11637 /usr/lib/ipsec/charon

But there is no internet on my device.

How can I troubleshoot my VPN connection? What and how to check?

Finally I grasp what happened. First of all I've checked the logs:

sudo cat /var/log/syslog

And there have found the error:

charon: 01[IKE] adding DNS server failed

I found that installing resolvconf handle this error:

sudo apt install resolvconf

It took me several weeks to fix this. May be it will save your time.