First---check your own bank account for the amounts you received for advance child tax credit payments between July and December. Add them up---do not rely on your memory. Then look at the letter 6419 you received from the IRS that showed the amount sent to you. If you filed a joint return, then look at the letters for both spouses.
How did you answer the questions about the CTC on your tax return? Did you enter the correct total received? What was on line 28 of your tax return? Was that amount the correct "second half" of the child tax credit you were eligible to receive? Or was the amount on line 28 overstated because you entered an incorrect amount for the advance payments?
Does the IRS show that you received payments that you did NOT receive? Check your online IRS account. Check the accounts for BOTH spouses.
https://www.irs.gov/payments/your-online-account
If you need to trace a payment that the IRS says has been issued to you, mail or fax a completed IRS Form 3911, Taxpayer Statement Regarding Refund.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
