There are a couple of issues that could happen when you try to watch an ad.
If you are seeing the screen below, where the button does not work, this means we're having trouble with our ads system. We are sorry for this, because for now, there isn't a solution, but our team is already working hard to fix it. :)
If you're seeing this screen below, you just need to close the game and open it again. This generally solve the issue. In case this keeps happening even after you reopen the game, you can contact us through this link, and we are gonna try to help you! :)