Unity IAP verify for non-subscription product

Please help me with understanding verifying purchased product.

I need to use it with Google Play Store, but it would be great if you add something about another platforms, also. if it's different.

Product does not consumes in game, it should be purchased once. And it's not a subscription because it should not be paid more than once.

I need to verify that product was purchased. I've found something about verifying in custom server, but I need to verify it without my server. I don't want to save data about is it purchased just in device.

How I tried to do it:
IStoreListener.ProcessPurchase with return PurchaseProcessingResult.Pending. Check it by IStoreController.products.WithID("product_id").hasReceipt. But it always returns false.

I also tried PurchaseProcessingResult.Complete but with same result.

What I'm doing wrong?