This is an old thread, but I’m bit surprised about the lack of a complete response to the original question. So for people with a similar connection, let me give it go:
Distribution networks use three phases. Usually that is three phase plus a neutral, but in some locations (apparently relatively common in Belgium and Norway) it is simply three phase without a neutral.
For a three phase 230 Volt systems with neutral there is 230 Volt on each of the phases (relative to neutral) and there is 400 Volt between the phases. The consumers are wired between neutral and one of the phases.
For a three phase 230 Volt system without neutral there is 130 Volt on each of the phases and there is 230 Volt between the phases. The consumers are wired between two phases. Usually one phase is blue and the other is brown. But the the blue wire is life and it will shock you!
For a consumer (like a light, an oven, your Shelly or Sonoff or …) it does not make a difference at all. They see a 230 Volt sine wave voltage either way. So they will work as usual.
On a system without neutral, typically you do not need to switch both wires. But be aware that with the switch off one wire is still life, and it will shock you. When switching only one wire some LED lights will not switch off completely due to leak currents. For exterior lights it is strongly recommended (or even mandatory) to switch both wires. A leak on the not switched life wire will trip your differential (GFI).
The three phase without neutral networks where originally used to save a wire (3 instead of 4 conductors) and thus cost. Meanwhile of course those networks run into power limitations (2/3). Not a good orignal decision (opinion).