macOS Sierra 10.12.6 can't connect to VPN using IKEv2. How to troubleshoot?

I am trying to setup a VPN connection using IKEv2. I fill in the server address, the remote ID and the user/password. When I click connect it tries to do it but immediately disconnects.

How can I find out what's going on? Where is the log file? I have configured one as indicated here: Troubleshooting IKEv2 on 10.11 El Capitan but the log file is created but empty.

Solution 1:

I had the exact same issue - turns out the VPN Server's certificate has expired.

Too bad there is not even a word in macOS about that, just an instant disconnect.

here's my thread: OS 10.13.3 IKEv2 VPN automatically disconnects