Some phones are failing on Notify with a 404 unauthorized. Grandstream are one of them. Basically the GS phone requires auth and PJSIP sill not send an auth unless outbound_auth is added to the endpoint config (outbound_auth=7000-auth)
See this Asterisk issue for details: https://issues.asterisk.org/jira/browse/ASTERISK-26694
The question is: Is there a way to get FreePBX to add the outbound_auth option to the Asterisk config files? Oristhe re a work around (for 150 extensions).
This is specifically an issue with the Commercial Endpoint Manager. It will not force the phones to update due to this issue.