Inside the extra folder there are actions for Steam VR 1.0. You can remove the newer actions and open the ones inside this folder if you wish to use the older version of Steam, BUT the main issue is that 2.0 with all the latest updates aren't working.
So I first installed Unity 2018.3.10 which is currently the latest version.
Next I went to the asset store and imported the latest version of SteamVR Plugin.
-> In Unity under window, you have to select SteamVR Input. And select Save and generate (found in the bottom left) This will install the necessary inputs that the toolkit will use.
Next, I imported the lastest version of playmaker. (And went through the install process with the welcome to playmaker window)
Last, I imported the latest version of Steam VR Playmaker which works with Steam VR 2.0.
I am running it now without any errors. I will work on a new video that will hopefully reflect the process better to go with the ongoing updates. Please let me know what issues you run into, which version of Unity as well. The latest updates only show on the latest version of Unity, which may also be causing the issue.
Thanks for the quick reply

I have done what you suggest, which did not work and I just tried in a new project again.
I am running the latest version of unity (Unity 2018.3.10) and installed the newest version of SteamVR through the Unity editor and Playmaker (Unity2018.3.Playmaker.1.9.0.p12). I have "Save and generate" the actions aswell, but I am still getting the 27 errors after installing your asset.
Also - [SteamVR Input] Saved actions manifest successfully. So the actions should have been generated.