Error Message: Offre : Cette offre n'existe pas et ne peut donc pas être mise à jour. Vous devez d'abord la créer.
This error means: This offer doesn't exist and thus cannot be updated. You must first create it.
It means that you are sending an offer (price and stock) for a product that isn't created yet on Cdiscount.
Make sure to check that no other error on this product is blocking its creation.
If there is no error on the product, its creation may be in process on Cdiscount's end - you may contact your Cdiscount account manager to have more information.
