[root@localhost ~]# ztcfg -vv

Zaptel Configuration
======================


Channel map:

Channel 01: FXO Kewlstart (Default) (Slaves: 01)
Channel 02: FXO Kewlstart (Default) (Slaves: 02)
Channel 03: FXO Kewlstart (Default) (Slaves: 03)
Channel 04: FXS Kewlstart (Default) (Slaves: 04)
Channel 05: FXS Kewlstart (Default) (Slaves: 05)
Channel 06: FXS Kewlstart (Default) (Slaves: 06)

6 channels configured.

Changing signalling on channel 1 from FXO Loopstart to FXO Kewlstart
Changing signalling on channel 2 from FXO Loopstart to FXO Kewlstart
Changing signalling on channel 3 from FXO Loopstart to FXO Kewlstart
Changing signalling on channel 4 from FXO Loopstart to FXS Kewlstart
ZT_CHANCONFIG failed on channel 4: Invalid argument (22)
Did you forget that FXS interfaces are configured with FXO signalling
and that FXO interfaces use FXS signalling?
[root@localhost ~]#