CDG and RER

Ticket machine or manned desk at RER B station.

Download the Bonjour RAPT app. Buy a ticket on it (to or from airport) Load on your phone wallet. Scan and go

There are ticket kiosks at both CDG RER stations. They usually have staff there to help with any questions.

https://youtu.be/nteUXuaSu7g?si=2zJ9qNCdzDSX6Qu9

Except now the cost of the ticket is €13 instead of the cost shown in the video

Our family of 3 took the RER to CDG. Many helpers at the ticket area. Be aware that it will take a long time to ride into central Paris. We purchased tickets like others have said in the special ticket machine area. You can que up and there are attendants to help.

Never let one of those helpful attendants handle your credit card, push the buttons for you or handle any money for you. A common scam is for a helpful with lanyard and official look credential to take your money and get your ticket and buy a child ticket and pocket the difference. If the person with the ticket is controlled which may well happen, the agent will fine them 35 Euro for traveling with the wrong ticket.

The machines have settings for English and are easy to use; be very wary of 'helpful attendants'

I know that helpful attendants can mean scammers selling you airport tickets, clandestinely selling your child tickets and pocketing the difference in price, but those at CDG's two RER terminals are actually employees.