macOS has a security feature called Gatekeeper that disallows installation of software that isn't from the Mac App Store or is from "unidentified developers". To disable Gatekeeper so Spine can be installed, please perform the following steps:
1.Open the System Preferences
- Security & Privacy
.
2.Click on the "Open Anyway" button next to a message, "Spine.pkg was blocked from use because it is not from an identified developer".
3.Select "Open" when an alert appears.
4.Then, the installer should open.