5th dnd – If I cast Friends trap on an enemy, can I curse him / Hexblade's spell without causing a fight?

If I throw the friends cantrip on an enemy, can I hexagon/ Hexblade curses them without causing a fight?

I guess I will not be able to remain invisible or not heard during the casting, but I guess the bottom of my question is:
Will the enemy notice that he has been cursed / cursed, and will this automatically provoke the fight?