It's very easy to create an account on the following portal and add money online: https://rie-saint-aubin.sohappy.work/
The web site is in French, but the screenshots below should help you create an account and use the web site
You just need to know your badge number. Note that this is NOT the CEA badge number, but the number that is on the printed receipt you get when you pay (so you have to bring this receipt back with you once). Click on Créez votre compte en quelques clics !, fill in your personal details to get something looking like the picture below, and validate by clicking on Créer mon compte.
Once you are logged in, look at the top banner and click on the rectangle at the top right to add money. You will then get to a page where you can select how much money you want to add (select the amount and click on Recharger mon badge) and then to a payment page. You will get a receipt by mail once the payment is validated.
You can manage your account by clicking on the 3 vertical points in the top right corner of the page, and selecting Mon compte. One of the panels allows you to enable notifications when the amount on your card goes below a threshold. The screenshot below shows the settings to get a notification when you get below 7 euros.
From the home page, you can also click on Se restaurer and then on Restaurant RIE St Aubin. You will find the following information on that page:
Note that if you don't want to contact directly the restaurant manager (you prefer the RIE council to anonymize your request), you can send a mail to
asso DOT rie DOT staubin AT gmail DOT com