Cannot download apps

1. Do you have a valid payment card on file as this is required even to download free apps?
2. Do you see a message that says "Your account has been disabled in the App Store and iTunes", there may be a problem with the payment method that you have on file.

When you see the message, don't try to edit any of your account information. Instead, contact Apple Support for help.

Source: If you see a message that says “Your account has been disabled in the App Store and iTunes” – Apple Support