Translation:We need to come to an agreement with the owner of the apartment.
Duo does accept both, but I disagree with the idea of replacing. Landlord implies renting the flat out, while the owner does not. You have assumed a certain context, when they are interchangeable, but I could think of other contexts.
E.g. my neighbour's flat can be used as a vacation property and be vacant for most of the time. (I've been in this situation, actually!) Given his frequent absences and the need for some common maintenance, there were certainly things we had to agree upon.