You are right, but when i’ve found the secret issue, i was fighting with a Ubiquiti USG 
As you can see here by default they seems to accept only the IP address and you can’t “easily” change, from the UI, the behaviour without messing with json and custom gateway (docs here) actually you can’t even use a ddns as remote peer on the UI.
I’ve mess also with ZyWall and other brands, and those parameters can be easily changed even from ui.