http://answers.unity3d.com/questions/1320861/android-build-commandinvokationfailure-unable-to-l.html
Android build CommandInvokationFailure: Unable to list target platforms. Please make sure the android sdk path is correct. See the Console for more details.
Upgrading to the latest does not work; that's what caused my problem :) They removed a feature and called it "Deprecated" without any warnings (this is not deprecation, it's removal).
The fix is to rename the "Tools" directory in the Android SDK.
Go to Unity, got to Edit->Preferences, then "External Tools"
Note where the Android SDK is located.
Go there, and rename the "Tools" folder to Tools-XXXX (replace XXX with version, or just call it Tools-Old). This is so you have a backup. You could just delete the folder.
Then, download this file:
http://dl-ssl.google.com/android/repository/tools_r25.2.5-windows.zip
Unzip it to the "Android SDK" location you found in the first step. Make sure it's "Tools".
Then, exit and reload Unity - build. It should work.
Also, thanks to @Vladimir-Niakhai, the MacOS version is at:
https://developer.android.com/studio/index.html
and look for "tools_r25.2.3-macosx.zip"
Credit to this thread on stack overflow: http://stackoverflow.com/questions/42538433/not-finding-android-sdk-unity and https://code.google.com/p/android/issues/detail?id=235455#makechanges