How can I redeem my past purchase?

First of all, please make sure you are signed in with the Apple ID account which you bought the upgrade with previously. Then, please, open the app, go to the “Add-ons” page and click on “Restore purchases” button at the bottom. After that all of your purchased add-ons will be restored on your device successfully.

If the issue still persists, kindly make sure you have a stable Internet connection, then log out of your Apple ID account, log back in and try to restore your purchase again.