Have you agreed upon the rent with the apartment owner yet? Yes this is correct 🙂. But it’s a little bit formal. I would say: "Have you agreed the rent with the owner yet?"

This is grammatically correct, but maybe a little awkwardly phrased?... So first, I would change "apartment owner" to "landlord" and "have" to "did". Then, I'd probably use "decide" instead of "agree", but let me show you how to say it using all three verbs. Decide: Did you and the landlord decide on the rent Did you and the landlord decide what the rent's gonna be? Agree: Did you and the landlord agree on the rent? *** gonna = a casual version of "going to"

This is correct. Upon is a little formal, but you can definitely use it, especially in writing. If I was speaking, I would be more likely to say “Have you agreed on the rent with the apartment owner yet?” I would NOT say “have you agreed the rent...”, that is not correct.