Adding your payment details is not quite irrelevant. The first 14 days are free of charge, so that you can trial our system. When you set up an account and install the app, you can choose when to add your payment details.
You can simply add your payment information by clicking on 'Settings' at the bottom left of the menu. A settings menu appears, where you can select 'Subscription'. Following that you will find an overview of how many profiles you have in the app and how much the subscription for the app will cost you. Here you can fill in your payment details. Choose a payment method and fill in your details.