How do you add a bank account as a payment method to Apple Pay?

You cannot add a bank account to Apple Pay. Apple Pay is a contactless way of using various credit/debit cards. You can add a debit card attached to your bank account but not directly from a bank account. You can only attach a bank account directly using the Apple Cash debit card administered by Green Dot Bank. Apple is not a bank and Apple Pay only supports valid credit/debit cards.

Both the Apple Card Mastercard credit card and Apple Cash debit card are administered by third party banks, not Apple.

You cannot add a bank account to Apple wallet for use with Apple Pay. You may be able to add a bank account for use with Apple Account in some countries.

Please review the Apple Support article I linked to below for the payment methods accepted in your country or region.

Payment methods that you can use with your Apple Account - Apple Support