How I can add my card ?

Credit Card details, used for payments, can be stored in potentially three places…

1) Your Wallet - where you can store Credit Cards registered for ApplePay:

Set up Apple Pay on iPad - Apple Support

2) For online payments when using the Safari Browser, credit card information is found in the Safari AutoFill settings:

Settings > Safari > AutoFill > Saved Credit Cards

Existing Credit Card entries can be removed by tapping the corresponding entry. Next tap Edit at top-right - and then Delete Credit Card.

3) Payment Card information that is associated with an AppleID account - used to purchase Apps, Subscriptions, Media and services via Apple - are managed from AppleID settings. See:

Change, add, or remove Apple ID payment methods - Apple Support

The instruction in the link below should help. Let us know if you have any other questions.

Add a payment method to your Apple ID - Apple Support