unity + app purchases + mac os X == mac DESKTOP app

USING UNITY 2020 .... I need to include: APP PURCHASES, in my educational application: ..... for MAC OS X .... in other words: .... this is an informative, educational application .... and ..... contains five (5) simple scenes in UNITY 2020 ..... in other words: the first SCEN ONUNITY will be free, but to access the other four (4) scenes or levels, the user has to buy them... by click with mouse on 3D buttons like the pictue atached. I REPEAT: I am using UNITY 2020 and my application is STRICTLY for desktop MAC OS X. I can share my screen with you to do it, achieve it, and show me how.