That has PME fault protection so one of two things are happening, the red indicator is indicating a PME fault or the unit is faulty. I think you are going to need to contact Garo or get professional help.
But it will be technically safe however you connect it. I'm pushing 60 so know how we used to do things but this change came in years ago but some people don't realise it or accept it.
This is an EN 60238 lampholder and the arrangement of the contacts and the construction of the lampholder make in non polarity biased, yours is like this I believe but a clearer picture at an angle may help.