I'm sorry I couldn't help you. I'm not quite sure what went wrong. Try searching for a video or two and check if your installation process of the game was correct.
Have you considered not decrypting the files? I suggest looking for a video on how to play pokemon fangames using joiplay since I am not familiar with the installation process.
I've made a change for patch 7.2 that will hopefully fix the issue. This error has been haunting me for a while now. Just wait for patch 7.2 to release then try again and let me know if it works.
The keybind on pc is the "Z" key. IDK about JoiPlay. You'll want to change the keybind to something you can use. The official name for the button is the "action" key. So set the "action" key to some button you have.
Try using JoiPlay version 1.20.015 and the RPG Maker Plugin for JoiPlay version 1.20.19. These are the versions players have confirmed work with the game.
Check if the plugins folder is intact and make sure it is not missing anything. Alco check your version of JoiPlay. I think the issue might have to do with how JoiPlay supports UTF-8 encoding.