The issuer of the 1099K is required to report and pay the backup withholding using Form 945.
In order to enter the additional withholding in TurboTax:
Please follow the steps below
1. Personal Tab
2. Deductions & Credits
3. Scroll down to Estimates and Other Taxes Paid and select Income Taxes Paid
4. Select Withholding not already entered on a W2 or 1099 (even though the withheld amount is on 1099-K - it is not an official form that requires separate entry)
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