How do I pay Apple pay with a debit card?

Hi, you can use a debit card (not credit card) to fund your Apple Cash card/account. Then use Apple Cash to pay your Apple Card MasterCard account. Here is a support link on Apple Cash,

https://support.apple.com/en-us/HT207881

Once you’ve added money to your Apple Cash account you can use it to make payments on your Apple Card. Here’s a link on making payments on your Apple Card account,

https://support.apple.com/en-us/HT209226

I hope this helps.