Even for free courses the user needs to be lgged in. To be able to log in you need to make sure your server is not stripping out authorisation header. This issue has been countlessly posted and fix shared many times in this forums. Unfortunately, this is a very server specific thing and out of scope of app support.
Please see important notes in this link : https://wplms.io/support/knowledge-base/quizzes-on-react/
this is the same fix you need in your site.