ipad as primary monitor for mac mini

Hi there. I'm trying to get my old Ipad2 set up as a primary monitor for my 2012 mac mini (i know, i know, living in the past!). It seems that people have managed to do this. I've got the Duet display app running and it works flawlessly when a hdmi monitor is attached to the mac mini and the ipad is displaying a second screen 'mirror display'. However, when i try and use the ipad on its own as a primary monitor (unplugging the hdmi monitor attached to the mac mini) it becomes glitchy. There are two cursors displayed and they make giant pixels appear wherever they go. Anyone managed to get this to work? I was reading about hdmi emulator dongles. Could this trick the mac mini to make it display the ipad as a second monitor (as it works fine like this) when there's not actually a monitor attached? any other ideas? I hope that all makes sense! Any help much appreciated. Thanks