IPSEC VPN with dynamic for remote firewall

[kapara]

I am trying to set up an IPSEC VPN tunnel between a OpnSense and a Unifi UDM-PRO.

On the OpnSense side it has the option to select a checkbox for Dynamic gateway but I can find no documentation on how to properly set this up.  Remote firewall does not have DynDNS and per information, I have found is not needed.

Is there any documentation on the proper setting for the P1 in OpnSense if the remote firewall supporting ipsec is using a dynamic ip?

Remote Gateway will not be correct because IP is dynamic.
Peer identifier is also an unknown so not sure what to choose.