Deductions & credits

TurboTax will automatically enter an offsetting negative amount for the 1099K that is reporting a personal item sold at a loss. Both the 1099K income and the offset will be reported in line 8z on your schedule 1. This has the same affect as putting the positive amount on line 8z and negative on 24z.  

To ensure your forms are updated properly start by deleting the 1099K entries in both "Other Common Income" and "Investments and savings"  You could also use the "Delete a form" function using these steps.

1. Select "Tax Tools" in the left hand menu
2. Select "Tools"
3. Select "Delete a Form"
4. Find the 1099-K and any other income form that doesn't apply (for example if a form 1099B was created for the income)
5. "Delete"
6. "Confirm Deletion"

Next,

1. Go back to "Other Common Income"
2. Revisit 1099K
3. Yes
4. I'll type it myself
5. Continue
6. Personal Item sales
7. Continue
8. Fill in the form information
9. Assuming it was one sale at a loss select "All items were sold at a loss or had no gain"
10. Done

Now to check to entries:

1. "Tax Tools" in the left hand menu
2. "Tools"
3. "View Tax Summary" in the main screen
4. "Preview my 1040" in the left hand menu

Check line 8z on your schedule 1.  You should see a positive and negative entry for the sale, labeled 1099-K personal items sold at a loss.

The amount in box 8z should not include the sale amount.