I can't go to the next level.

I can only use one level at each course. Other levels are locked. When I want to learn them, I get information about purchasing a subscription. Please help. 4th day I do the same exercises. Everything works fine on the website. Unfortunately, the above problem appears on the IOS application

You need to purchase a subscription to unlock the next levels from the Memrise provided courses. Go to decks.memrise.com to get user-provided courses that are free.