As I recall, with the APIs for both Android and iOS it is possible to determine if a non-consumable product already has been purchased.
It would be great if this would be possible with SDKBOX IAP also.
If possible, it would be nice to have such a field in the sdkbox::Product struct.
I think it is confusing for the user to be presented with a login screen for the store when entering the app, before even considering to buy anything. I would not recommend doing it that way.
In the shop I have a “Restore purchases” button, which invokes sdkbox::IAP::restore().
However, this is something quite different from the functionality i requested in the original post.