It doesn't work properly on joiplay anymore but I'm pretty sure this particular issue isn't your fault. They had an update that broke compatibility with a lot of games
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If you downgrade back to the older JOIPlay and RPG Maker plugin versions from here, it should fix the issues. (Not sure if using the older version causes issues with other games though.) https://www.patreon.com/joiplay/posts/joiplay-1-20-611-137694579 I also heard, but didn't confirm, that there was some sort of patch to fix the issues on the discord for JOIPlay.