A CP10 Notice means the IRS believes you made a mistake on your income tax return and owe more. The refund you asked to apply towards next year’s estimated taxes is now lower.
Why does the IRS send CP10 Notices?
The IRS sends CP10 Notices for miscalculations. You may have missed a step when completing your tax return, checked the wrong box, or entered something in the wrong line.
What if I’m not sure if the IRS is right or I disagree?
The IRS may not always be right. In addition, just because you made an error doesn’t mean you truly owe that tax. The IRS may agree that you don’t owe money after you fix the error and/or supply additional documentation.