Please note that you could only add the card from the checkout page when you are paying for an order. If the card option is not available for you, then card information cannot be added and you can only pay with TT.
Refer to below steps to add a card:
1.If you have not bound a credit card or bank card before, please refer to below picture to add your card and fill the card information.
On PC:
On APP:
2.If you have already bound the card before, please refer to below picture to add your card and fill the card information.
On PC:
On APP: