This usually means the data files are in the wrong folder. Re-check Step 4 to ensure the data is in the correct path.
Because this is a fan game, it is not available on the Google Play Store. You must allow your browser or file manager to install external APK files. Go to Settings > Apps > Special App Access . Tap Install Unknown Apps . sonic megamix mania download android install
Fan games change hosting platforms frequently due to updates. Look for the official release threads on reputable community hubs: This usually means the data files are in the wrong folder