Good, at least they allowed you to sell one item. That appears to be typical of the online marketplaces, they use a “pump and dump” strategy to coerce you into buying advertising. You should see an upward trend then nothing. When you hit “nothing” you are suppose to panic and buy more advertising… I would not worry about the promotion that is just losing money for you.
See how the sales progress, when you start taking market share from others you will be attacked. Take that as a sign of success. Just deal with that then move on and stay guarded.