@SailSaulbrious
Yes. I use Relay 1 on the Cerbo (Any ordinary switch would do the same as @JohnC notes). Then the Cerbo relay is to wired to Aux 1 positive and negative of the Quattro. I use 1 programmable assistant to switch on AC Out 2 and a second programmable assistant to switch it off, depending on the on or off signal sent by the Cerbo (which I control via Node Red).
The old forum has a post on wiring parallel inverters. I will see if I can find the link.
F.