Hopefully this helps future visitors find the apartment, especially those who have not visited France before -
The entrance to the courtyard where the apartment is located is easy to miss. There are a set of metal doors between Hotel Montparnasse St Germain and Le Delices du Kashmir, enter the provided building code and those doors will give you access to your Airbnb.
When we arrived there were some electrical issues that needed addressed, Leo immediately took care of these and ensured we had a pleasant stay.
The 6th Arrondissement is an incredible place to stay. This is a safe, walkable area surrounded by many incredible boulangeries and only a few minutes from the Jardin de Luxembourg.
I would absolutely stay here again.