mikrotik openVPN config

Hi,
I am a newbie in mikrotik. I am trying to configure openvpn in my mikrotik device. Mikrotik is behind the ISP router Only the router has a public static ip address. So I am going to forward port 443 from ISP router to mikrotik. In such scenario during the creation of the certificate what ip should I put i the certificate, the public ip of the ISP router or the private mikrotik ip?
Thanks

Public IP.

But the public ip belongs to the ISP router. IS this ok?

It is the first known public location of your network.
Why wouldn’t it be ok ?

Besides, if you think it should be private IP, why did you bother to ask ?