"Today dinner is on me."
Translation:Oggi offro io la cena.
True. That's because "dinner is on me" is an idiom in Englis- IE, the dinner is not literally "ON" you, but rather you're paying for it.
Would "Io pago PER la cena" be incorrect? (duo accepts "io pago la cena" which sounds to me as if it is missing a preposition..? Unless it's an idiom?) Grazie.