I just installed Unity 5.5.1f1 and I cannot set my platform to Android because I don’t have the requisite supporting package. That’s fine, I click the button to open the download page, download the .pkg (I am on OS X) and the installer fails. It fails every time, I tried downloading the pkg again, no change in behavior. There is no meaningful error message produced, and I don’t know where to look for a log file or way to see what is going on.
I DO have available disk space to install this package. There are approximately 75GB free on this machine.
I have attached a screen cap: