In order to get the mod to work you need to roll CK2 back to 2.7.2
Normally you can't go further back than 3.0.1 so you have to follow these instructions from this post and you will be able to unlock earlier betas and be able to roll back to the required version.
Link to post - https://steamhost.cn/steamcommunity_com/app/203770/discussions/0/1734339901253848647/

Hope this helps those that are stuck!

Thanks you, SckMyLeftNut!