Update to 16.70

I have the Garmin Montana 750i using a Mac.  I have tried updating to 16.70 to no avail.  I tried the unit by itself after it was connected to my iPhone and WiFi and it will not update.  I have restarted my unit many times...still no update.  I am able to sync with my iPhone and did all the updates in the iPhone.  Still no update.  Any reason for this?