joining to courses

I have 2 categories of users and I want cat 1 user to be able to join a private course without having to add them. We should be able to add conditions to join a private course (for ex they must have a specific fluent crm tag).
I made a little plugin to do that: I put a link in the personalised lock screen but the blue join this course button is always visible and generates an error msg when clicked 😒