Hello and welcome!
To get the best feedback on your item, you would have to present clear pictures of the marks. They look too blurry on my monitor to make any comment. However, in terms of style, this item doesn’t appear to be early 18thC from the north of France. Also, looking at the underside, it seems to me that the chalice is not hand-raised. Again, better pictures would help. Does the dealer claim that the paten is the same date as the chalice? The engraving on the paten is 19thC style.
Good luck in your ongoing research!