JoiPlay current version 1.01.430 is broken
You can either downgrade to version 1.01.400 and disable auto-update in the playstore
https://www.patreon.com/posts/joiplay-1-01-400-51867946?l=en
Or you can enable beta builds in said playstore and use 1.01.500
There is a new beta, 1.01.630, which once more doesn't work though
Also, make sure you have the RenPy plugin too
If you have further problems, try the JoiPlay Discord