Currently, spacedesk Business License is available for Android Viewer only. All other Viewers (Windows Store, Apple App Store) can still be used for free until Business License will become available in their app stores, too. To purchase Business License, just open spacedesk Viewer on Android > click on the floating menu > click on licensing (FYI: The price for the initial purchase can also be found on this page.) You will then see the button “Purchase Now” which will direct you to the payment method via Google Play.
More details about prices can be found by clicking the link below the “Purchase Now” button.