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.
See -> Buy additional app features with in-app purchases and subscriptions
Buy additional app features with in-app purchases and subscriptions
See also -> Apple Media Services Terms and Conditions
Legal - Apple Media Services - Apple
See -> Resolve a problem with your payment method
If your payment method has expired, declined or failed, or a message says "There is a Billing Problem with a Previous Purchase"
See also the following Apple articles:
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.
Add money to your Apple Account balance
Add money to your Apple Account balance - 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.
If it is not dlear, get support and assistance -> Spain
or Call direct to -> 900812703