Is project.json inside a subfolder (like myproject/project.json )? If yes, move everything up one level so the folder looks like:
: Locate your new .zip file. Right-click it and rename it, changing the .zip suffix to .sb3 .
This method works if your SB3 was simply "mislabeled" as ZIP by the OS.
If the project logic is broken, you can open the project.json in a text editor (like Notepad++ or VS Code). Look for the "targets" array to ensure your sprites and scripts are intact. If the JSON is malformed (missing brackets or commas), use a JSON validator to identify and fix the syntax before re-zipping.
Make sure all images are in .svg or .png and sounds are .wav or .mp3 .