When running the package installer, MacOS provides a generic “The installation failed.” message without additional information as shown below.
I’m documenting this for posterity and search results in case someone else encounters it. Someone recently reported this and we discovered the issue, so I wanted to capture the issue, the troubleshooting, and the solution.
The installation troubleshooting page has detailed instructions for how to retrieve the flox installation logs that are located /var/log/install.log and see if there are additional details. In this particular case, the MacOS FileVault was interfering with the /nix/store mount process. Often this is addressed by rebooting as it was in this case where that fixed the issue and the install was able to complete.
package_script_service[1858]: ./postinstall: error: failed to bootstrap /nix
package_script_service[1858]: ./postinstall: If you enabled FileVault after booting, this is likely a known issue
A similar issue was discussed here.