The above answer is correct.
I can add one more twist.
I filed a paper 2019 Tax return, on the due date in Oct 2020.
I received an IRS paper receipt and ALSO I signed into IRS.gov to look at my return AGI.
In both cases the AGI listed on the paper receipt and my IRS.gov account matched the paper return.
But I still got rejected. I then noticed that even though I turned the return in on time (paper), the receipt and the website said that it was processed sometime Feb 2021!
So then I changed my 2020 AGI for efile, to "0".
Yes, it worked!
From my experience your AGI is wrong according to the IRS database, then no amount of changing pins will help (I tried that first 2-3 times, with the AGI I had used in my return, always rejected). The pin is so that you can use it to get information in the future, in case you forget your 2020 AGI.
So if you are constantly getting rejected
1) Make sure you're not using an amended return AGI like the other contributers say. If you efile for 2020 and it still rejects
2) Check to see if you are using the correct original return AGI from the IRS.gov website. If you efile for 2020 with the correct 2019 AGI...and it still rejects:
3) Check to see (from the IRS.gov website) when your 2019 return was processed. If it was after November, I would definitely try putting in the AGI of "0" (no matter what the IRS website currently says your AGI was)
Option 3 was the only one that worked for me.
