If you try to use your debit card when there is not enough money in your account to cover the transaction and your account does not allow overdrawing, the transaction will be declined.
Could I use it to charge my wallet and then subscribe using the wallet funds? If that doesn't work you will possibly just have to delete you account and create another which is allowed if you are willing to go to that effort and see if that solves the issue.
But, she remains fascinated by the tiny land of tall people.