AC500 dual charging from grid

I have two AC500 units with 4 B300s batteries. I’m running in split phase off of PV running heavy loads through a transfer switch. How do I best grid charge both units simultaneously during the off peak hours without disrupting my AC output during those hours? I keep getting error codes. Any suggestions would be helpful for those cloudy days

@Jeffb06175 May I know the error code? Could you please share some pictures of your connection and settings?