are you sure that FB generated a 1099K? The 2021 rules required $20,000 AND 200 transactions for it to be issued. Whether or not you receive a 1099K, you are required to report your income.
were these personal items or items you purchased and then turned around and sold?
if personal items, and you sold them for less than your originally purcahsed them for, that is not taxable income and is not reported on your tax return.
