Love the app but... Ive purchased the key on another app store. Now  the app doesn't work on that app store. If I download the app from Play  then the key should be transferred here as well. Edit: If so  then put a functionality in the app that with entering the code  user can get full version activated. And that code can be shared by you as you have already received payment for premium services through other app store. There are many apps which allow full version activation based on code entry.
October 14 2016