Since there has pointedly been no reply from the business man author to this message string one can only assume:
There are 2 licenses;
1) The first one was about $5 a couple of years ago when this app was getting started.
It only works for the device it was first installed on.
2) The second license (the "unlocker") is more recent and is $15. It is said to work on multiple devices - probably, until the next license comes out.
Thus, someone who bought the first license and got a newer device must pay twice to get this app on the newer device.
Interesting business model - penalize older customers.