IPSEC VPN from Android on 6.4.3

I seriously tried everything but can't get it to work: IPSEC VPN on Android phones.

I used the wizzard to create a native VPN and Mac and Windows clients connect without any problem. But Android isn't working. I tried diferrent Android versions (7 - 10) and the build-in and fortinet client. With the android build-in VPN it tries to connect and after a few seconds it shows "Unssuccesful"

With the FortiClient it says: Sorry, could not start the connection "VPN" Error: Could not establish session on the IPsec daemon.

Is this a problem in 6.4.3 OS ?