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First, open the App Store app and swipe all the way to the bottom of the page. Tap the "Apple ID" button (It should show your Apple ID in the button).

Next, tap "View Apple ID" and log in using your App Store password. If something is wrong, you'll be notified to rectify it at this point. Sometimes it's an expired credit card, missing code, etc.

You can also go to "http://appleid.apple.com" with the email address and password you use for the App Store and ensure there are no issues there. If there are, you'll be prompted once you successfully log in.