Arcane feedback

A target you can see must make a intelligence saving throw against your spell save DC. On a failed save the target losses a first level spell slot and takes 2d6 psychic damage on a successful save the target doesn't loss a spell slot and takes half damage 

Up casting the spell allows you to make the target loss spell slots up to the level you cast it 1 first level at first level, 2 first level or a second level spell slot at second level and so on.

If the target doesn't have any spell slots at that level or non at all than the target only takes the damage on a failed save.