There are some reasons if you got a 404 error when access a lesson/quiz page. Below are two common reasons:

The first reason is setting the wrong permalinks. You should set your permalinks is Post name in Dashboard => Settings => Permalinks => choose Post name.

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The second reason is that you didn’t publish that lesson/quiz/course.

If the 404 error reason is none of the above reasons. Please create a topic on our forum: LearnPress support forum. We will check your issue.