Dear @meethos,
all you need is an external relay with 230V capable coil - the HDO (DSM in English according to the wiki) is a 230V AC signal. The relay will then switch +24V DC from your power supply which will go to a DI of Neuron.
An alternative way is to use a smart energy meter like this one: https://www.unipi.technology/smart-energy-meter-pro380-modbus-p40?categoryId=16 right behind the main switch and also connect the HDO signal to it. Then you will read all the information which the energymeter provides (like the current voltages, frequencies and total power on all three phases including the HDO status)