using UNITY 2020 and XCODE 10.1 for (IAP) in app purchases

I have an EDUCATIONAL application only, it weighs nothing and is very basic: (on Unity 2020)
In my app (informative education), it includes five (5) scenes in total.
the first is free to access the other four (4) and buy them inside the application.
In other words, if the user wants to access the following scenes or levels, ...
access the first scene for free,
But to access the rest you must buy them with (IPA) IN APP PURCHASES.
I need this project only for DESKTOP MAC OS X.
(mac store only)
and I am using UNITY 2020.
There is any tutorial or some help please.
Thank you