After a Tariff Plan has been created, you can select „Assign Billing Plans”. For this, you can find a button in the upper side of your screen.
In the middle you will a list of children, arranged by groups. Each child has, on the right side, a button which helps you select the Tariff Plan you need. Pressing the button will open a box from where you can choose from already existing versions of menu.
This way, billing will be made based on the Tariff Plan chosen by the parent, without any confusions.