How to restore non-consumable offline

I'm pretty much ready to release my first game. But my IAP implementation right now is not completely functioning as I want, and given that involves monetary transactions, I really don't want to get this wrong.

My game just has one non-consumable IAP that removes ads and unlocks the full game. My current implementation is working except for when the user opens up the game in airplane mode or is offline. The non-consumable purchase is not activated.

I'm validating the receipt successfully when online, and doing so in the OnInitialized function. But when offline, that doesn't get called.

I found this link and tried to follow the process to do local validation. But my script never enters the PurchaseProcessingResult function.
https://docs.unity3d.com/Manual/UnityIAPValidatingReceipts.html

If this is a simple question or has been answered, my apologies but I just haven't been able to find an answer. How do you validate local receipts when offline so you can give the user their non-consumables?

Edit: Game is only going to be released on android right now

 

Thank you. I've been absolutely convinced that "Local" receipt validation must have been something that can be done offline. I'll get creative in coming up with a solution for these cases.

 

A restore uses the Google Billing Library and connects to their stores. You can award your user any products that you choose to persist locally via receipt or other storage, but that would not be a store-based restore operation.