I’m just talking to myself here but the option has now appeared! Yay. Much joy.
Do you mean the Add/Remove Controller feature has appeared on the Qolsys panel? What is your panel’s Z-Wave firmware version? To confirm, navigate to Settings > Advanced Settings > About > Z-Wave.
As of Z-Wave Firmware 6.81.03 this is no longer a supported feature and the issues may occur if attempting to pair.
The PIN it is likely looking for is an S2 Z-Wave pin, which may not be applicable in this case.