CP268 tells you we made changes to your return because we believe there is a miscalculation on your return. You get an overpayment credit when your tax payments exceed what you owe.You'll automatically receive a refund of the credit. You can find the CP or LTR number on the right corner of the letter. You received this notice because the deposits or payments applied to your account didn't agree with what you claimed on your federal tax return. Your options to address IRS Notice CP128. Notice deadline: 21 days. Let the IRS know of a disputed notice. What this notice is about. We corrected one or more mistakes on your tax return.