In 2021, Kathleen, a single taxpayer, received a distribution of taxable income from her traditional IRA. Kathleen normally makes every effort to file a timely and accurate return, and she filed her 2021 tax return as required. However, she forgot to bring a copy of the Form 1099-R, reporting information about the IRA distribution, to her tax appointment. Therefore, the income was not reported on her 2021 return. If Kathleen does not take action to correct this error, which of the following IRS notices is she most likely to receive first?