1 connected the first one R320 and ran through the setup wizard, set it as the master
I am now trying to add a 2nd AP (R550), but when I power it on, it does not connect to the master. it appears just to do nothing. if i connect to the configure.me network it just says "building the unleashed network. it may take a few minutes", but it never progresses past that point
Are the APs connected via a wired network? In order for the 2nd AP to find the master, I think that it has to use the wired connection to do so. Can you double check that the connectivity is on the same physical network?
Check the AP in question separately (without master). Reset it to factory settings and if you can't access it than, something is wrong with this AP. If you can access it when reset and alone, check firmware version and country setting, and try to reload different Unleashed version (newer or older, doesn't really matter). If still doesn't work, RMA AP.