You have been a victim of what some of us more experienced aroid growers call a node-flipper.
I am not sure you will be able to salvage this. But, never say never. The rot seems to have gone into the meristem and hollowed it out.
If they had been generous enough to give you at least one more node above the leaf you would have had a better chance.
Be honest...did you buy this from overseas? Or from a seller here in the US? (who probably imported it from overseas and almost immediately resold it).
All of these cuttings that people post photos of and ask for help with look exactly the same. They are the same diameter, the same cut (one node, maybe one root if they did not remove that).
You will have the best chance of success if you treat the plant with a fungicide like Captan, or alternately buy some Auxin (Rooting hormone) that contains fungicide. The most commonly available in the US is RootOne-F.
Moisten the cutting in water and dip the WHOLE THING, where all those cut off roots are, in the powder, shake off any huge excess and place it in damp sphagnum. Keep the moss 'just damp' not wet.
See that thingie that looks like a sort if eye in photo 3? That is likely your next new root. Make sure you get some Auxin on that.
Keep it in bright light, keep it warm, do not use a heat mat or put it in a plastic bag but do try and keep some good air circulation around it. With luck, and a great deal of patience, you may get this to work. If it succumbs anyway, you will at least have tried.
I can offer you this graphic, which was made by some fellow aroid growers who moderate aroid forums to address just this specific situation that you find yourself in. It may be 'too little too late' because the information would have been more valuable before you committed to the purchase, but if this cutting fails and you decide to buy another, it may help you in the future.
Welcome to the site, and I am sorry that your first post had to be about this! If you have an interest in aroids, there is a small group of us on the Philodendrons and Monstera etc forum who would welcome your participation.