Under VPN/SSL VPN/SSL VPN Server, i press export Certificate. ovpn file is created. I import it to openvpn, but... certificate is not properly imported. I can see it is embedded in ovpn, but openvpn is expecting p12 file. 

Windows client is 10, 64-bit, latest version of openvpn. 

Can you help out what are the proper steps to make ssl vpn to work?

How to establish an SSL VPN Server by Omada Router in Controller mode?（Controller V5.4 or Above） | TP-Link

needs to be reviewed and update so that it works with latest openvpn (at least windows, but would not hurt for linux info to be there too).