Are you sure the file is a valid zip file :). If you’re downloading the file then I’m assuming you’re getting it after it has been placed in as an artifact of the build, so it’s possible you’re trying to run the butler command before the zip file that eventually makes it into build artifacts is ready.
I recommend looking over the order of things to make sure it’s happening as intended. You can also try extracting the zip in CI in place of the butler command to verify that there’s a valid zip file at that path at that time