There may be some confusion setting in here.
1. Are ONLY those circuits fed through the inverter/charger not working, or are other things like roof A/C not working. If only inverter/charger fed circuits not working, indeed look at the on-inverter breakers. But, if A/C's not working as well (i.e. whole 120 VAC system down) then the ATS OUT and breaker box IN connections are a good place to start.
An, the "salesman switch" is 12 VDC. Unrelated to the 120 VAC system, unless the thermostats for the roof A/C are 12 VDC, etc.