Applepay

If you mean your Apple Card you cannot pay it from another card in your wallet, you can only pay it from Apple Cash or your bank account→How to make Apple Card payments - Apple Support

Sorry, your post is a bit confusing.

Apple Pay is the mechanism you use to pay for things in stores and online. It uses your own cards to pay for anything you buy through Apple Pay. There is no such thing as an Apple Pay bill. Apple Pay doesn't generate bills. All payments are charged to credit and debit cards added to the Wallet app.

If you used one card to pay for something, and you want to use another card to pay the first card's debt, that is called balance transfer, and it has nothing to do with Apple Pay. You would need to contact your card issuer and work out a Balance transfer from one card to the other.

You cannot. The Apple Card does not support balance transfers to other credit cards directly.

You would need to get a cash advance from the card you want to use to pay, add the money to your bank account or Apple Cash, and then use that to pay the Apple Card bill.

There is no possible way to do that. As explained by Phil.