EGO Smart Heater with openhab via Rasperry pi4

Hey Friends, i need some Help with my EGO Smart Heater.
Raspberry 4
Ego Smart Heater with Modbus ( LAN )
thats the configuration.
I installed all of them. Heater is in Tank (filledwithwater) Power and lan is connected. Indikator lamp works.
In my Fritz box i read the ip of the heater.
On openhab i installed Modbus addon. I can read the actuall temperature. Works fine. Now i wanna send him the that i have enough Energy and he should start to Heat. It dont work.