Do you encounter any issues with the app? Probably they are already answered in the FAQ. Have a look on it.
Clear the cache and data of Play Store. Via “Manage apps” stop the Google Play Store app, clear its data and cache. In gReader/News+ press Menu -> More -> Check license. Don’t forget to turned on your internet connection.
Sometimes Play Store does not work correctly. Just wait for some days and try it again. Also check the account for your Play Store. You might not use the same account you have bought the app with.
NOTE: If Upgrade to Premium is not shown in the Menu then the license is accepted.
Couln’t you find answers in the FAQ or in the Forum? Leave us a message with the contact form.