Yes, you are right eBay was not required to send you a 1099-K, but they can. If the error in your 1099-K is causing the items to be a gain (gross amount of payment is more than your cost), you should ask for a corrected one.
Since they did send you the form and your items were all sold at a loss, here is what steps you need to take in TurboTax Online:
- Within your tax return go to the magnifying glass icon on the top right, type 1099-K and select the Jump to 1099-K link in the search results
- Choose Add a 1099-K
- The next screen will ask "Which type of income your 1099-K is for?" choose Personal item sales, then Continue
- Enter the information from your 1099-K
- After you choose continue, the next screen will show "Personal Item Sales". Here is where you choose "All items were sold at a loss or had no gain"
