Hi,
I dont think it’s good UX practice to make users think a course is free, only to find out halfway that course material is locked and you need to upgrade to access it.
This just makes me less inclined to actually sign up because I feel tricked into starting something I cant fully finish.
It might be me who missed some communication along the way regarding this, but marking a course as free and then limiting access to course material makes for a really bad user experience - regardless of whether or not you write it somewhere beforehand. Apparently that effort is not good enough.