You can access this feature on the page Manage my payment methods.
Feedbooks is based in France, where it is illegal to store a credit card number. We strictly apply the law. Feedbooks stores an authorization, which is not a card number. This authorization allows the customer to be able to make a new purchase without having to enter the card number again.
Even if the authorization number were to be intercepted by a third-party, in no instance would it grant access to the credit card number nor would it allow to make a transaction toward another bank account.
This payment system is safer than asking the card number for every purchase (which would potentially increase the risk of interception).