Debit cards are enabled only in selected geographies. This is because of number of fraudulent sign ups that involved debit and prepaid cards so they are disabled.

You should use PayPal if is it available to you. PayPal requires to pay in advance (to get a credits) to to use services. Minimum payment via PayPal is $5.

If PayPal is not available for you, or you have other questions/problems, you can contact Support team. They will be happy to help you with this.