Thanks for being a customer. In order to qualify for the credit, you need to update to the newest version of the Amazon Appstore. You should be prompted to upgrade when you open the Appstore. If you aren't prompted, please follow these steps:
1. Find and open “Amazon Appstore” on your device.
2. Go to “Settings” > “Version and Release Notes” to ensure you have version 7.5 or greater of the Appstore. If you have an earlier version of the Appstore, please tap “Check For Update”.