2024 rules reference for Armor of Invulnerability.
Armor (Plate Armor)
You have Resistance to Bludgeoning, Piercing, and Slashing damage while you wear this armor.
Metal Shell. You can take a Magic action to give yourself Immunity to Bludgeoning, Piercing, and Slashing damage for 10 minutes or until you are no longer wearing the armor. Once this property is used, it can't be used again until the next dawn.