Apple Pay is not used to download apps so not sure what you are talking about. Apple Pay is used in physical stores and websites. It has nothing to do with Downloading apps.
Do you perhaps seen its asking you for a payment method to be added to your Apple account?
If so, yes, a valid payment method is required to make use of the App Store services, including downloading free apps and updating existing ones.
If there's. spending charge or some other issue with our account now, it will prevent access to said services and you will need to add a credit or debit card to your account to resolve the issue. There is no way around this at this point.
You must add a payment method.
click here ➜ Add a payment method to your Apple Account - Apple Support
Once added, and if no other issues are present, and you have no active subscriptions, you should be able to remove the payment method from your account.