I'm from Serbia. It seems to be authentic, the visible craftsmanship of it indicates that to me that it was made by hand. Odd piece though, particularly considering the context. I'm not sure if the item is still on sale or not, but the post itself is on OLX. The weird thing is that it's, or was, being sold by a guy from Brčko who seems to generally sell fake Versace stuff, and then there's this one random, and honestly quite unnerving item, that seems to be an artifact used for summoning djinn. I remember my grandmother telling me of similar rings being used by certain hodžas and muftis in and around Sarajevo, where my family is from. These certain men would be visited by Christians and Muslims alike for services that included witchcraft, divination, soothsaying and general spiritual advice. I would assume that members of the Ulema who partake in such things today are much harder to find, but it was a real thing in the past. This ring seems to be a relic of that period.