The Mac OS X 10.9 Mavericks download script is now hosted on Mavericks Forever. To download Mavericks, open a Terminal on any Mac and run:
curl mavericksforever.com/get.sh | sh
Or, navigate directly to mavericksforever.com/get.sh to read what the script does.
Basically trying to fix what Apple broke , when you download the installer app from the old App Store , it can’t validate the InstallESD.dmg but the one your script downloads is valid . Trying to merge the two together to create a working .app is proving tricky. 🤦🏻♂️🤦🏻♂️