It looks like this controller is an 8-bit controller based on Arduino according to this snippet taken from this site. Hopefully I’ve identified the correct machine.
Controller Software: The Genmitsu 3018-PRO uses Grbl, high-performance open-source software for controlling movement, and runs on Arduino.
In that case $30 = 255 would be the correct value. You would then want to make sure that S Value Max in LightBurn Device settings is also set to 255. It defaults to 1000.