Invalid Android SDK directory?

I have been scratching my head here trying to get my android SDK to be recognized by Unity. I can’t for the life of me figure out what unity is specifically looking for. I have downloaded the latest SDK using

$ sdkmanager "platforms;android-27"

but that doesn’t seem to matter to unity as it doesn’t recognize it.

sdkmanager --version
Unity Version
OS: Mac OS X
version 10.14

I had the same problem, and could not really solve it. Yet, by uninstalling the sdkmanager and then installing the huge, heavy ‘android studio’ I managed to build. I wish sdkmanager had worked.