Mains (230v) is connected to "L" (live) and "N" (neutral) and the voltage regulated device is connected to "1" and "2".
"1" (white) is connected to the live wire (brown) and "2" is connected to the neutral wire (blue).
The voltage regulation happens on the neutral side (grey/red).
What I cannot understand is why the live wire (white) is also connected to the coil. Isn't this connection redundant?
Documentation from the manufacturer: