View and manage your subscriptions here:
View or cancel app subscriptions on iPhone - Apple Support
It may have been determined that your payment method is no longer valid. That could happen if a previous transaction was unable to be processed or if you disputed a charge on the payment method. To view your Purchase History, look here and see if there are any charges that are showing as Pending or has not been able to complete.
View your purchase history for the App Store and other Apple media services - Apple Support
You will need a valid payment to download apps even if they are free. There is no charge to download the free apps, but the payment method must be from the same region as the region set on your device. This is how they verify you are using the correct App Store and prevents users from just changing the region on their device to download apps or use services that would normally not be available to them.