We used a 0 too and it was accepted. I am guessing that this issue is with the IRS. I suspect they have not yet loaded the 2020 return's AGI into the file where it can be used to verify the 2021 returns. My guess.
The IRS is way behind! We filed an amended return for 2019 in April 2019 and we still have not received our refund for that year after almost 2 years.
Cheers, Larry
