Tiamat and spell immunity, DnD 5e

[teffe]

The stat sheet for Tiamat says she can ignore spells of 6th level or lower. If I were to cast a lower-level spell, say Magic Missile, but use a 7th level spell slot to cast it, would it count as a 7th level spell, and damage her? Or would it count as a 1st level spell and fail to damage her? omegle xender

[Zacchaeus]

The level of the spell is determined by the spell slot used to cast it. So your Magic Missile would be level 7.