The number of FXS extensions (analog extensions) is determined by the number of S2 modules (one S2 module contains two FXS ports, i.e. 2 FXS extensions) and SO modules (one SO module contains one FXS port, i.e. 1 FXS extension) installed in MyPBX. So if you need to add FXS extensions, please make sure that there are empty module slots for S2 or SO module first.
Step 1: power off or unplug MyPBX.
Step 2: unscrew MyPBX, and open the upper case.
Step 3: insert the S2 or SO module into the corresponding slot and place back the upper case and tighten the 4 screws. Then power on MyPBX and new FXS extensions will be added successfully after rebooting.
