Ok I checked your site using the credentials shared on another topic.
I found out your wplms-customizer.php file is empty, there is no code present, refer:
http://prntscr.com/c4q4pg
So now I added the code in the file and still it didn't worked, so to debug the issue I tried to print some value in the take this course button but its not showing anything. This seems to be a caching issue may be server caching so try clearing all type of caching and specially the server cache and then check.
I checked the code and it works fine on my test setup so it should work on your website also, just try clearing the cache.
Let me know if this helps.