KDE 6 fingerprint unlock

The KDE 6 announcement says that

On prior versions you chose between either password or fingerprint authentication for the lockscreen. In Plasma 6, both are supported at the same time.

I've updated my Neon install, what do I need to do to enable this? I've set up a fingerprint through the user settings, but when the screen is locked I still have to use my password to unlock - there isn't a prompt, and touching the reader doesn't seem to do anything

Edit: follow up on an old post in case someone stumbles across it - I needed to install libpam-fprintd