How do I use my Apple for online payment? Do
How to use my Apple Card for online purchases
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If you are using Safari and the website uses Apple Pay, you can pay via Apple Pay. For other browsers and for sites that don't use Apple Pay, pay by using your card number. See the following from How to make purchases with Apple Card - Apple Support
Pay with your virtual card number
If you need to give a card number when you check out online or in stores where Apple Pay isn't accepted, you can find your virtual card number in the Wallet app. If you use Apple Card Family2 and you share your account with a co-owner3, you each have your own virtual card number.