TLDR;

The required App ID is gnddkmpjjjcimefninepfmmddpgaaado 

Steps to install the Chrome App / Extension using the admin console.

Step 1) Log into admin.google.com

Step 2) Navigate to Devices -> Chrome -> Apps & Extensions -> Users & Browsers

Step 3) Hit the yellow '+' circle (bottom-right)

Step 4) Select the Chrome Icon to 'Add from Store'

Step 5) In the 'Search By ID' box paste the APP ID: gnddkmpjjjcimefninepfmmddpgaaado

Step 6) Hit Select.

Step 7) Click on directprint.io Printing, select 'Force install' under installation policy and hit 'SAVE' (top right), no need to Pin to taskbar

These steps will deploy the application to your Chromebooks.