First review the IRS notice carefully against the filed tax return. Figure out where the difference is and see if the IRS is correct. Chances are the difference is line 30 of your form 1040 which is the credit for the stimulus payments you did not get in advance. The IRS is checking anyone with an amount on line 30 against their records of the payments that went out. So if the IRS is correct then your only option is to pay the bill.
