we found the quickest way to implement ATJS using GTM was to have the ATJS code hosted in a file somewhere on our website and than create a GTM tag to call that script on we wanted to load Target-- it than reduced the size of the GTM tag as the ATJS code is a large file
alongside setting up workspace and assigning properties in admin console, you also need to assign property on the first test that you do, using the 'settings' icon