You probably need to call for support. XML_Admin doesn't sign in to the forum at all and doesn't appear to troubleshoot or respond (reference your week old post previous this one).
I can't give any official answers, but I would assume it isn't supported, you would need to create a VPN to do it most likely, it is only meant to work if the mobile device and MFP are on the same LAN, due to the discovery process and SNMP/IPP.
There is a Mobile link Knowledgebase
And some documentation
Almost all the documentation lists that it supports only up to Android 5.1, which is untrue, it supports officiall Android 7.0, and iOS 10.
It works in Android 7.1 as well.
What ports need to be opened up on a router to allow MobileLink to discover a Xerox mfp beyond the local subnet? I've checked the documentation on Xerox Support but don't see technical information listed. This ties into the request for a Security White Paper for the App that I posted last week.
Jeremy A Thompson
IT Solutions Consultant
US Channels Unit