I had 2 versions of Mono installed, one via Homebrew, the other downloaded from Mono website (http://www.mono-project.com).
This was causing issues with versions, so I tried removing both.
I uninstalled Homebrew with
brew uninstall mono and the other one with
sudo rm -rf /Library/Frameworks/Mono.framework sudo pkgutil --forget com.xamarin.mono-MDK.pkg sudo rm -rf /etc/paths.d/mono-commands
(as per website instructions.)
I then re-downloaded and installed the latest package from http://www.mono-project.com. It installed successfully, but when I try to
mono from Terminal, I get
/usr/local/bin/mono: No such file or directory
brew unlink mono and
brew rm mono, but still nothing.