Some of the symbols are slightly different. Under a magnifier some of the fleur-de-lis look poorly hammered. Also is 0.5mm thickness which makes me question if it is genuine. Diameter is 28mm. Weight is 2.6g.
I don't know French medievals as well as I should, but can point out that the legends on this coin do not begin with a cross (instead it is something like the Breton ermine tail?), and they end with an additional letter n:
SIT : nOmЄn : BЄnЄDICTVm : n : (tail?)
KAROLVS : REX : FRAnCORVm : REX : n (tail?)
I acquired this piece when I first got into numismatics. The more ive learned as why I've gotten skeptical about this one. It is quite thin. And the way some of the markings appear.
It is a later reign.
I am sure if the question has been posted on French side of Numista it would have been solved in an instant.
Coins from this era are usually very thin. Maybe one of our French colleagues can comment on authenticity (I see what you mean about the workmanship in some areas)