I searched for similar questions on this issue but found none related to Mac OSX.
Situation:
Trying to test android apps on a Galaxy S (D
This may sound crazy, but I tried every suggestion on this page except what finally worked:
Use the Samsung USB cable that comes with the S7 (my S6 cable worked too)
Every other USB cable I tried did not work. I don't know exactly why (USB 2 vs 3?), but that is what worked for me.
Of course, make sure USB debugging is turned on, and yada yada yada, but I did all that and still NOTHING. The moment I plugged in the USB cable that came with my S7 I got the RSA fingerprint message, and confirmed USB debugging, and the device showed up in Android Studio when I clicked Run.
HTH --jsp