The root of the problem is that the inverter is a Power Jack.
There are internal adjustments for cutoff and alarms on most inverters. If you got a repair manual with the inverter, it may show where the trim pot is. There is an review of one of your units on youtube. The buyer had to do some repairs straight out of the box and was a bit suprised that the maker included a repair manual.
The specs I see on eBay say the alarm goes off at 29v and the unit cuts off >30v.
If that is the correct range I would still consider that too low for a lead acid battery bank. Our forklifts need
at least 30.6v for a weekly equalize.