I have 2 EG4 wallmount allweather batteries with it. The system is only about 3 months old, so I'd say both ...

390 volts

What batteries do you have with your system? Did the errors recently start, or have they been happening since you installed the system?

If you need a main control board, I may be able to assist with that. Have you confirmed that the issue is with the main control board?

What voltage are getting on the DC input on the Mini Split?

Is it possible to get (RS-274-X, BOM, pick&place file) so i can have PCBway to build me a new circuit board as of right now that seems to be my on...

Whoops. Flexboss inverter, not 18 kPV if it makes a difference ...