Go to Settings→ PBX→ Extensions, click “add” in the extension edit page.
Tick “FXS” in “type” and choose the FXS span port.
1. Extensions on S-Series VOIP PBX can be “SIP”, “IAX” and “FXS” at the same time.
2. If the extension has ticked “FXS”, you must assign an FXS port for the extension. If the FXS port in the drop-down list is RED, it means the FXS port is being used and you cannot choose this port. If the port is BLACK, it means the port is idle.