For payment through a Debit/Credit card, you will need to verify your email ID. Please follow the procedure for the same.
1. Go to 'Buy Credits'.
2. Click on 'Proceed'.
3. Enter all the details (credits you want to purchase).
4. Fill your Address and other personal details.
5. Click on 'verify your email ID' and you will receive a verification mail on your registered ID.
Choose 'Verify now on your email ID where you received the mail regarding verification and then you can make your payment through Debit/Credit card.
And now try making payment. :)