cannot use arcgis online webappviewers in essentials

hi, our arcgis online portal folks have started creating webappviewers.  i cannot seem to add those as a reference map in my essentials sites.  here is the link:

http://blm-egis.maps.arcgis.com/apps/webappviewer/index.html?id=e124205491964d83bec143eea55b4b38

is there a trick to this?  i am essentials 4.2.1, do i need a later release??  i would appreciate some suggestions.

Jeff