Stupid question - Kubuntu 20.04 detecting Huion 420 tablet, but can't draw with it

Hi everyone, as the title says I'm sure I'm doing something stupid. My Kubuntu 20.04, Plasma 5.18.4, kernel 5.4.0-29-generic laptop (which is fairly beefy with 16 gigs of RAM and an i5) is detecting my Huion 420 drawing tablet since I installed the DIGImend driver from here.

If I open up tablet settings, I can see that the tablet is detected as a Huion 420 and modify its settings. However, drawing on the tablet does not cause anything to happen. I have also confirmed that it appears under xinput.

Any pointers for what I'm missing?

Edit: I tried disabling/enabling the touch tool with super+ctrl+T ... no luck.