Restore can't work. I've looked at their code for the C2 plugin and I know why restore has never worked.
On Purchase Completed triggers Consume Purchase for Android & Finalize Purchase for Apple.
Both of these tell the server your item is consumed, gone from the queue/account. So Google/Apple cannot restore it.
The On Purchase Completed trigger should be split into TWO types, 1 for unmanaged consumables and another for managed non-consumable that doesn't trigger consume/finalize.
The reason Ludei's own apps work with consume is they don't make it with C2, they control their IAP triggers manually.
I'm using cranberrygame's IAP plugin for XDK and he has trigger for unmanaged & managed with a consume trigger that you call in yourself manually when required. Restore works if you do not consume the item.