Why is my Pixels Print On Demand App not working?

I have been using the Pixels Print on Demand App successfully up until a few days ago. When I attempt to open from the Apps menu I now get this page

This site can’t be reached

Check if there is a typo in undefined.

DNS_PROBE_FINISHED_NXDOMAIN

I’ve tried the fixes suggested with a google search, but to no avail. Any suggestions?