I did not receive advance Child Tax Credit payments during 2021 for a qualifying child. Why could that have happened

There are several reasons why you may not have received advance Child Tax Credit payments during 2021 for a qualifying child:

1. New Qualifying Child: If you had a new qualifying child during 2021, such as through birth or adoption, you may not have received all of the advance Child Tax Credit payments for that child for which you were eligible.
2. Qualifying Child Claimed by Someone Else: If your qualifying child lived with you for the required period of time during 2021 but was claimed or could have been claimed as a dependent on someone else’s tax return for 2019 or 2020, you may not have received all of the advance Child Tax Credit payments for that child.
3. Lack of ITIN: If you did not have an IRS Individual Taxpayer Identification Number (ITIN) when advance Child Tax Credit payments were made during 2021, you would not have received advance payments.
4. Child's SSN: If your child did not have a Social Security number (SSN) valid for employment when advance Child Tax Credit payments were made during 2021, you would not have received advance payments.
5. High Income: If your modified adjusted gross income (AGI) was too high on the tax return that the IRS used to determine your advance payment amount (either 2019 or 2020 tax return), you may have received no advance Child Tax Credit payments or reduced advance payments.
6. Main Home Outside the U.S.: If your main home was outside the United States for more than half the year, you may not have received advance Child Tax Credit payments, although you may still qualify for the Child Tax Credit when you file your 2021 tax return.
7. IRS Processing Delays: If the IRS had not processed your 2020 tax return when determining the amount of your advance Child Tax Credit payment, they may have used your 2019 tax return information. If there were discrepancies or delays in processing, this could have affected your advance payments.
8. Non-Filer Tool: If you did not use the Child Tax Credit Non-filer Sign-up Tool in 2021 and the IRS did not have sufficient information from your previous tax returns, this could have impacted the issuance of advance payments.

If you did not receive advance Child Tax Credit payments, you can still claim the full credit amount when you file your 2021 tax return during the 2022 tax filing season.

Sources:
IRS FAQ
IRS FAQ
IRS FAQ
IRS FAQ
§ 24. Child tax credit
IRS FAQ
IRS FAQ