Approval of a charge is done by you when a subscription is started, including a free trial that automatically becomes a subscription if you do not cancel. That is done on the Approval Screen that requires you to double click the side button showing the subscription price, subscription start date, and for a free trial the length of that trial. There is also an important message there that says to avoid further subscription charges, you should cancel a day before that renewal date. If you agree to those terms, then after double clicking the side button, Authentication proceeds with Face ID/Touch ID or Passcode.
You have agreed to pay for the subscription and also agreed to cancel the subscription to avoid the charge. If you don't do that and the charge was not able to be processed on the payment method you have chosen, then you owe the amount you have agreed to pay, and you will not be able to continue to use the App Store for any reason until that is done. You are responsible for your own actions.