Hi Eugenio,
Sorry for the late reply.
I did check it, and it looks weird indeed. Both params (i.e. add-to-cart and cpn) work properly when used separately, however, add-to-cart seems to be blocking cpn for some reason when used together… Could I log in to your site to check what’s going on (my email is [email protected])? Please let me know if sharing an account is not an option, and I will continue solving it remotely.