How do I transfer Apple Pay money to my debit card?

You can transfer money from your Apple Cash card to either your bank account or debit card. Here is the support article that will help you accomplish that.

Transfer money in Apple Cash to your bank account or debit card - Apple Support

By Apple Pay money, I assume you mean from your Apple Cash card, and the link that was provided will allow you to do that. Apple Pay is simply the technology on your device that allows NFC payments managed by the cards in your Wallet app. You cannot transfer money from a Credit card to your debit card, but any money you have on your Apple Cash card can be transferred to either a bank account or debit card.