Are you using the Review link on the lessons page? Those are not using the spaced repetition, and do not require flashcards.
The website infers your progress based on the flashcards you added through the Manage page. Add cards there. You may use the SRS or not, but the cards must be added to see the progress bars on the lessons page.
Non-SRS based lesson reviews have been added. Just click the Review link next to each lesson in the Progress page.
Using "Review" to refer to both SRS and non-SRS "reviews" could easily be confusing for some users. Probably the difference could be made more evident by calling non-SRS reviews "Cramming", both in the Lesson list and the "Cramming" section.