You might encounter this scenario in several specific situations:
This usually happens when you create the ZIP manually. Use an actual Scratch project (exported from the editor) as a template. Compare your ZIP’s internal hierarchy to a known working SB3 (renamed to ZIP). zip to sb3
Since Scratch 3.0 launched in January 2019, projects are saved as . Under the hood, an SB3 file is not a proprietary binary format; it is simply a ZIP archive containing JSON data, sound assets (WAV or MP3), and images (SVG or PNG). You might encounter this scenario in several specific
: This usually happens if the files are inside a subfolder within the ZIP. To fix this, extract the files, select them all directly, right-click to Compress to ZIP file , and then rename that new archive to .sb3. Since Scratch 3
To truly master the process, try building an SB3 from nothing:
I can give you exact steps or a small script for your case.