I would ask to you what I have to do in this situation.
I have an old UWP App that I have started to porting to Xamarin.
The old App was a App for fee (not free). This new one will be a free App, but with In-App products to purchase.
What I would like to do is that: if a user has purchased the old App, when he/she is going to update you App with the new one, it will get the update and ALL the In-App products.
Is it possible handle that in some way?