Are you using the Joiplay version from the Play Store? If so, that version is no longer updated. Use this version:
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. The renpy plugin you need is the 8.2.3 version (8.2.1 also works) to play this game but the new version of JoiPlay also has a plugin downloader you can use. If you have other Renpy games on your phone that require the Renpy 2 version then you'll need to edit this game in JoiPlay. Hold on Corrupted Academy until a menu pops up, select Edit, at the bottom in type change it to Renpy (Python3) and hit save. The game should work correctly when you start it up. Hope this helps.
EDIT: Just realized JoiPlay is no longer available on Play Store. So everyone should be getting JoiPlay from their Patreon page now or at least updating it. A lot has changed with the app.