The iPhone App is an enterprise app which you will need to approve following the steps outlined here.
iPhone
Version: 1.11
07-Sep-2018
Click this button on your Phone
iPad
Version: 1.11
07-Sep-2018
Click this button on your Tablet
For Android you will need to allow installation of apps not from the play store, as shown here.
Android
Version: 1.08
17-May-2018
Click this button on your Phone or Tablet