In order to view mature series, you have to go to Tapa's website, Tapas.io. After logging into your Tapas account, click on the discover tab and there should be a mature button you can click on

After you click on the mature button, you'll have to enter your age in order to access the series. After verifying your age, you can view any mature series you want. If you want to read the mature chapters on Tapa's app and get the One Tap discount, you have to subscribe to the series on the website and the series will show up under the Subcribed button found in your library. I'm not sure if I'm allowed to tell you that, but oh well.

The bonus ink in your account can only be spent on Tapa's app and this includes free chapter unlocks as well. The one tap discount is also only available on the app. If you're new to Tapas and still have some chapter tickets left, those can only be used inside the app.