I already purchased the Advanced Feature Set (AFS) for another device. Do I need to purchase it again for my Mac?

The features that make up the AFS are different on each platform (Android, iOS, Mac OS, or Windows) on which PocketBible runs. They are sold separately. The fact that you own the AFS for Android or iOS doesn't mean you own them for your Mac.

The Advanced Feature Set is optional and need only need be purchased once for each operating system (not once for each device). For example, if you own an iPhone and an iPad, you only need to purchase the Advanced Feature Set for iOS once, since both devices run PocketBible for iOS. But if you also own a Mac, you'd have to purchase the Advanced Feature Set for the Mac separately, if you'd like those features enabled in PocketBible for Mac OS.