Owntracks: ip in host

I installed the Owntracks-addon.
The host-information that is given by the add on is somewhat like http://192.168.x.yyy/api
A ‘local’ ip-address… so if I’m outside with my smartphone, how can it communicate with my home-assistant that is hidden behind the router?

In some examples I see a myhome.duckdns.org-ip address.
That makes sense, but I didn’t install duckdns at the moment.

I have Zerotier installed.
My smartphone is in the same network as my hassio.
Can I use the Zerotier ‘ip-number’ (provided that I connect my smartphone to the Zerotier network?