Bewitching Smite

The target must succeed on a Charisma saving throw or have the Charmed condition until the spell ends. At the end of each of its turns, the Charmed target repeats the save, ending the spell on itself on a success, and taking 2d4 necrotic damage. 

Using a Higher-Level Spell Slot. The damage increases by 2d4 for each spell slot level above 1.