I have grandstream HT813 for my home setup. for test purpose I used PISIP extension configuraiotn for grandsteam FXS port and it registered without any issue. then I used FXO it also registered with VitalPBX SIP trunk. then I changed the FXS extension. then From that onwards it went to unregister and never got back to register mode for FXS. i tried to change the local default sip port for fxs and fxo ports . the result is same. FXS port never came back to registered status.
kindly note im very new to vitalpbx. I have latest vitalpbx(3.x) installed in VM