How do I transfer wallet money to Apple Pay

Apple Pay is not a payment method and you cannot add funds to Apple Pay. You can use credit cards and debit cards in your Wallet app to make purchases. If you’re in the US, you can use Apple Cash (prepaid debit card) to make purchases.

So, the money you want to transfer, is it in a bank account and do you have a debit card associated with the account? Do you have a credit card account?