Hello:
I test with FreePBX-13 and centos-7. After check and enable the modules from modules management.
the GUI can not show the modules and no action for further process. 
-------One more thing, when i run systemctl status -l freepbx.service, show errors----
[root@localhost ~]# systemctl status -l freepbx.service
freepbx.service
Loaded: not-found (Reason: No such file or directory)
Active: inactive (dead)
[root@localhost ~]# asterisk-r
-bash: asterisk-r: command not found
[root@localhost ~]# asterisk -r
Asterisk 13.5.0, Copyright (C) 1999 - 2014, Digium, Inc. and others.
Created by Mark Spencer markster@digium.com
Asterisk comes with ABSOLUTELY NO WARRANTY; type 'core show warranty' for details.
This is free software, with components licensed under the GNU General Public
License version 2 and other licenses; you are welcome to redistribute it under
certain conditions. Type 'core show license' for details.
=========================================================================
Connected to Asterisk 13.5.0 currently running on localhost (pid = 3109)
localhost*CLI>