The target takes an extra 2d8 Radiant damage from the attack. The damage increases by 1d8 if the target is a Fiend or an Undead. Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 1.
+1d8 per slot above 1; +1d8 extra vs an Undead or a Fiend.
RollQuest ships the D&D 2024 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.