I hope that someone who owns this ring will weigh in. I would expect “Tiffany & Co.” to be spelled out and either “PT” in a sans serif font or “Pt” in a serif font.
Also it’s hard to say from the angle of these pictures but the prongs seem off to me.
I’ve read about issues with authentication at Poshmark specifically and other similar sites; I would want to verify any purchase I made on my own.
I’ve seen Tiffany Victoria pieces imitated tons of times (there are posts on this board about how to make similar items, which of course no one would resell as real, but I mention it to show how popular and copied the designs are). But @Bron357 makes a great point — the ring is either diamonds and platinum or it’s not. If you verify the materials and you paid a fair price for a ring of that quality then enjoy your ring!