@ sting4s
When efiling your 2021 return, be sure you verify with the 2020 AGI from the original 2020 return, not an amended one. If married filing jointly, both spouses use the same total 2020 AGI--do not divide or otherwise allocate it.
If you filed real late last year, such as after October 2021, or if your return was delayed by the IRS for a long period of time and wasn't processed prior to November 2021, then you can try using an AGI of 0 (zero.)
Or try this if this is your situation:
"If you used the Non-Filers tool in 2021 to register for an advance Child Tax Credit payment or third Economic Impact Payment, enter $1 for your prior year’s AGI on your 2021 tax return."
