Most reliable transport app from a Paris apt. to CDG.

I suggest the G7 taxi app BUT morning trips (6-10 AM) should be booked 1-2 days in advance as demand is high.
It's the app I use all the time. The fare to CDG is flat: EUR 55 (right bank) or 62 (left bank) + 7 booking fee.

G7 will get you a real taxi

I agree with the suggestion of G7. Why? They have never canceled on me ever. And as a real taxi, they have access to the bus lanes which Uber does not. I suggest that given that you are staying at an apartment that you be outside 5 minutes before the scheduled pick up time, especially if there is no convenient spot for the driver to pull over and wait for you.

we do this at least twice a year and have for many years and always get a G7 taxi; they have always arrived a few minutes ahead and always been reliable. I phone on the English speaking line two days ahead to book the reservation. I used to book the night before but a couple of years ago they didn't have a cab available, so now I do it two days ahead. It costs 7 Euro to reserve but this is imperative for an airport run; you cannot count on one last minute. the price is fixed. 62 from left bank and 55 from right bank.

Apartments are not more difficult than hotels for this; we always stay in an apartment and have never had a problem with taxis to the airport. I still build in an extra half hour because I am that way -- but we then always have too much time at the airport.

G7, reserving a few days ahead, as everyone here has said.