I have configured CUPS on Ubuntu 18.04 server. I can print (from iPads and Macs in our school district) from the network as long as the device is connected to the same vlan. after a week of research and experimenting I still cannot figure out how to print from a device on a different vlan. We can route between vlans so it has to be in my configuration. My brain is fried.
Have you the IPP (afaik 631) port allowed?