Ok ... you failed to report the 1099-B from the broker on the return ... the basis for the stock you sold was reported on the W-2. So it seems you only reported the W-2 and now the IRS needs the form 8949 & Sch D filled in as well. Good news is that you will have a loss on the sale for the amount of the broker's sales fee.
It is all income to them since they only got notice of the SALES price and not the cost basis ... you need to report the cost basis on the Sch D which you must not have done because they sent a CP2000 notice. Again the fix is easy ... fill in the 8949 & Sch D and mail it back to them as directed.
you can try talking to your broker to see if they know anything. this is a public forum. we can't see any of your documents. if your broker can't help them I suggest
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