Loading a custom protocol mapper

I am trying to create a custom mapper and I used this example keycloak-extensions-demo/tokenmapper at main · dasniko/keycloak-extensions-demo · GitHub

I created a jar from the file and put it in the providers directory for keycloak 18.

The issue is that when I start keycloak in dev mode I do not see in the list like you see in the video Keycloak - Custom Protocol Mapper | Niko Köbler (@dasniko) - YouTube

Am I doing it completely wrong? Been hunting around trying to find an end to end example for 17/18 but I cannot find one.