I tried a other workaround:
- I added OpenVPN Net-to-Net testn2n connection on “ipfire server”.
- Downloaded and unziped Client Package from “ipfire server”.
- I added and properly configured the connection testn2n as a client on “ipfire client".
- I replaced testn2n.p12 file from Client Package
in /var/ipfire/ovpn/certs/ on “ipfire client".
It looks like it works.