Can't Connect Odroid XU4 to HA App

No luck so far connecting the app to my new device, with HA already loaded.
I can see the device on my network, and ping the IP successfully.
The app – iOS on tablet and iphone – doesn’t find it. Successfully connects to the HA
observer IP (not sure that does me any good.) I’ve tried connecting with the
homeassistant.local:8123 as well as with the IP address, with and without the 8123 attached.
All give the same error code: NSURLErrorDomain - 1004
Could really use some help. Thanks.