Innogy over Openhap 2 to Homekit -- Siri Problems

I have some problems connecting Innogy RST thermostats to Homekit via OpenHab 2. I have integrated the thermostats and can also raise and lower the temperature via the slider. However, the thermostats cannot be controlled via SIRI. SIRI accepts and confirms the command to increase the temperature. However, the command is not executed at the thermostat. Does anyone have an idea?