This board is not suitable for direct control from an OpenHAB GPIO pin. It expects inputs as phase angle control. that means each input must be turned on (and off) during each mains power cycle, that is to say 100 times a second. The timing of that after the AC power zero crossing determines the delivered power.
It is intended for use with some dedicated controller doing that work hundreds of times asecond, say an Arduino with appropriate code. A subsystem like that could also listen for an occasional command from OpenHAB, say “channel 1 50% dimmed”, and maintain that state all by itself.