Password for tests

Hi! I need that some of the parts of my course we’ll be available only for users that paid for it. For example quizes. I made quizes visible only after password entered. But the problem is that there’s a button downside to start a test and it makes available to enter a test without password. How can I solve the problem? Thanks!
https://cdn1.savepice.ru/uploads/2019/11/24/1bc968f71443be9037dbc647fd4bf0f5-full.jpg