I'm the guy who kicked off this thread.
The attempt to enter ZERO is when you are asked to state your 2019 AGI. Apparently the IRS uses the 2019 AGI to verify it's really you who is submitting your 2020 return.
So it has nothing to do with your declared 2020 AGI.
Good luck in trying to submit using the ZERO. I had to go to the Post Office and submit via paper.
