@AndyB-airband, to debug why the SM is not getting onboarded into cnMaestro, it would be helpful to isolate the problem to either the SM configuration or the mobile device's connectivity to cnMaestro.
When you navigate to the cnMaetro UI's Onboarding queue, do you see the SM? It should be at the top of the table. If so, this implies that the SM was properly configured and has network connectivity to connect to cnMaestro. The problem lies in the mobile device's connection to cnMaestro to initiate the onboarding command.
On the other hand, if you do not see the SM in the onboarding queue, then the debug should focus on determining if the SM has the correct configuration so that it can establsih a network connection to cnMaestro. From the SM's UI, you should be able to run a ping test to cnMaestro, DNS lookup test to make sure gateway/DNS IPs are configured correctly, view the SM's "device agent" (cnMaestro) log, etc on the SM. Refer to the knowledge base article below for some debug tips.
http://community.cambiumnetworks.com/t5/cnMaestro/Device-On-boarding/m-p/51484#M19