To be able to enforce VPN on public apps, you will have to perform a few additional steps.

  1. Navigate to Apps & Books > List View.
  2. Select the Public tab.
  3. Select Add Application and add an Android app or Edit an existing Android app.

  4. On the Deployment tab, select Use VPN and then select the  Per App VPN Profile client you created above.

  5. Save & Publish.