App & desktop combo project

[Colin Holgate]

I don't think the letting them use the file on iOS if they paid for it on desktop will work out, unless you put in a feature into the desktop one that gives a link to the iOS app, maybe using custom URLs?

As for the normal in-app purchasing system, you don't need to keep track of things. When the user does a reinstall of the app (as opposed to an update), you can give them an option to restore old purchases. You then ask the app store if that person has paid for that item, and if they have, it's downloaded again.