After having my federal (and therefore state) return rejected since the AGI for 2020 included in TurboTax didn't match the IRS records, I put in "0" for the AGI. It's hard to find - all the way at the end when you are about to hit "send". After three other tries using the actual AGI, the "0" option worked! (BTW, it actually tells you to do this on the IRS website, but it is buried. I found this fix in a Washington Post column.)