After buying the full version, I tried to download and install the android version, first play protect tries to stop to install, but even if I ignore it, it says that the application was not installed...
After trying multiple installers I finally found the error. It is that the Game's signature does not match the demo's signature, so it cannot install on top of it.
I believe, as much as it feels like when your gameboy ran dead in the middle of a pokemon fight, that you have to remove the demo to install the fuller version. I did that and it stated that my app had installed instead of the opposite.
Chewy pushed a new Android version on it so he's working on it for sure. Give him some time it's a very small operation they have. Check out their discord for updates and have some patience, I'm on the same boat after purchase. As a software engineer, I know the struggle... It'll stabilize. Discord: https://discord.gg/QSGE7p
I am having the same issue as well... I do not want to delete my saved file. I just finished buying the game....