Use the document Add a payment method to your Apple ID - Apple Support to review your payment methods such as credit or debit cards.
On a mobile device:
1. Open the Settings app.
2. Tap your name.
3. Tap Media & Purchases, then tap View Account. You might be asked to sign in with your Apple ID.
4. Tap Manage Payments.
Check there are not any problems with your payment method. They will usually appear in red lettering. If there are, make sure what you have entered is correct. If it is, contact your financial institution. Problem methods will usually have a notice in red lettering below them. The article: If your payment method is declined in the App Store or iTunes Store - Apple Support has some information about declined payment methods.
If you cannot see a reason for a problem and you have contacted your financial institution, you may find the fastest route to resolution would be to contact Apple for assistance with this.
Apple's official support articles present multiple statements about requiring the presence of a payment method at times, even for free items. If you are encountering one of those situations then based on the documents I suspect you have no option but to enter a valid payment method if you wish to continue downloading. Read the support article Add a payment method to your Apple ID - Apple Support about how to do that. The payment method may not be charged if you also have account balance or the item is free, but the payment method has to be present. This next article lists valid payment methods for different countries but note that in this situation Apple Account balance alone apparently may not meet the requirement and you need to use another payment method until you find one that satisfies Apple's requirement (often a credit or debit card): Payment methods that you can use with your Apple ID - Apple Support .
To contact Support, do this:
1. Click on this link --> Choose your country or region - Official Apple Support
2. Select your country
3. Select: Billing & Subscriptions
4. Select: Subscriptions & Purchases
5. Select: Update payment method
6. Select a chat session or a phone call.
