what type of inverter and battery have you got?
A BMS communications failure means the inverter can't talk to the battery
If you have a gen 1 inverter then the BMS data cable, the thin black cable between the inverter and the battery can come loose in the bottom of the inverter as the plug doesn't have a latch to hold it in position. You'd need to unscrew the 4 screws holding the cover in place and plug it firmly into the right socket (check the inverter install guide). There are two that look identical, but only one will clear the BMS error on the portal. Then ideally support the cable so the weight of it doesn't pull itself down out of the socket. I cable tied mine to the other wires to support it