If you have purchased an Add-on and you reinstall the app or install the app on a different device, you will need to restore your purchases. In some cases, you will need to restore your In-App purchases after the app was updated to a new version.
Note that purchases are bound to your Apple ID. If you log-in on your new/different device with a different Apple ID, you will not be able to restore purchases. So be sure that you are using the same Apple ID that you've used to purchase the Add-on.
👉 To restore your purchases, tap on the menu icon.
👉 Tap on "Add-ons" below
👉 Tap on "Restore purchases"
You may need to enter your password for your Apple ID.