What happens when Wall of Illusion is attacked while facedown?

When a monster attacks it does it flip up and activate since it was attacked? or does it only activate if it was attacked while faceup?

Anyone has an explanation on how Wall of Illusion's effect works?

the only thing that wall needs is being touched (going through damage claculation), everything else doesn't matter

So it's like saying when it simply battles?

Yes it doesn't matter if it's attacked face-down it will flip-up in damage step and its effect will activate.