Does anyone know if this place still exists? I’ve been trying to make a reservation for an airport transfer and the website isn’t working.
The website is operational. As you've already found, it just doesn't show the ability to book transfers to/from CDG to/from Paris city; only to/from the suburbs or between CDG and Orly. Viator once sold this company's transfer on their site but doesn't currently, and there hasn't been review since 2019 so it's possible it's not a service Paris Webservices offers anymore.
https://www.viator.com/tours/Paris/Private-Transfer-from-Paris-Airport-to-Paris-City/d479-7245P12
(I wouldn't advise anyone use Viator for bookings; just thought it relevant that the service isn't available though them either)
Editing to add: YAY for Pam (below)! I'd follow her advice any day so you're in good hands! :O)
If you are in a hotel they should be able to make a taxi reservation for you. Taxis are perfectly safe for solo women travelers (guessing you might be a solo female traveler!).
You can also download the G7 app to your phone and book a taxi on that the day before for the airport. You will be charged a premium over the flat rate to the airport for booking ahead. I've always had the drivers arrive a few minutes early. Book for 4 hours before your flight.
Since taxis started charging a flat rate to and from the airport, it’s not surprising that a transfer service would now focus on the suburbs.
From the airport, taxis from the official taxi stand. Drivers are not tipped.
To the airports, we use Bolt, but FreeNow is also good. Just download the app.