You can download free apps, but you may need to have a valid payment method on file, even if the app you want to download is free.
Free apps has also In-app pruchase.
My payment method is not working and there’s money on it.
See the following Apple articles:
If you can’t download or update apps on your iPhone or iPad
If you can’t download or update apps on your iPhone or iPad – Apple Support (UK)
👉 Add a payment method to your Apple ID
Add a payment method to your Apple ID – Apple Support (UK)
Add money to your Apple Account balance
Add money to your Apple Account balance - Apple Support
If you need to change or update your Apple ID payment method
If you need to change or update your Apple ID payment method - Apple Support
Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.
If you need to change or update your Apple ID payment method
If you need to change or update your Apple ID payment method - Apple Support
If you still need help, get support from Apple directly -> Get Support or call Apple in your region see -> Contact Apple for support and service or check -> here for more support and assistance.