When I test each negative pole of the two against neutral, they each show 120 volts AC. However, when I use a voltmeter to test from negative to negative (line to line), I get 0 volts. The expected result is to see 240 volts.
I have also measured the voltage between both negative buses on the circuit breaker against each other and got 0 as well. However, they are just a continuation of each other. I have used a double pole breaker with a jumper between both poles to bring the inverter's AC output to both buses.
I suspect that is my problem but I don't know how else to do this.