I have used my Debit Mastercard regularly to do online shopping. Since July 2016 I am no longer able to do so. It is a's if my service from Standard Bank have been downgraded. If my Debit Mastercard cannot do online purchases why was I able to do it previously.
If this trend continues much longer I will have no alternative but to change banks. That will be unfortunate as I have always been with Standard Bank.
I'd recommend you check for the below things:
1. Ensure you are using the right debit card number which is printed on your debit card.
2. If you're using the right debit card number and still facing the issue, I'd suggest you remove and add the payment method on google settings.
Also, I'd suggest you check the settings of your Google Payments account to make sure your address and other billing information in the payment method provided are up to date and match the information in the personal information.
If you are still unable to add your debit card to your account, I recommend you contact one-on-one support team of google for better assistance.
Let me know if this helps.