Adolf It's a bit complicated as far as I understand but definitely not impossible. If you pay with bank giro you can use auto giro for automatic transfers. I've also noticed email reminders during my beta subscription that comes around a week before my balance hits $0.
That means a week to process a manual payment. Today most phones also have calendar functions where you can add reminders and the dashboard even calculate the exact date and time for you when your balance will hit $0.