Analysis: Grid voltage too low
Solution: 
1. Check what the phase voltage is and frequency is from the display, check if they are in the rated range.
2. Check if AC terminal and distribution box internal connection is correct, check if any connection is loose or disconnected, check if the breaker in distribution box was tripped.
3. Use the multimeter to check if the grid connection is correct, and check if phase voltage and line voltage is too low
4. Check if the inverter’s safety code be set correctly and Grid under-voltage protection point be set to match actual situation.
5. Waiting for a while until grid voltage recovered, to observe on inverter and check if it can automatically return to normal running.