Both my federal and state returns were e-filed and were rejected. I use the CD download version. The explanation was my AGI did not match what the IRS shows. The problem is I did not e-file my 2018 return. On two occasions TurboTax Support told me to delete the AGI amount printed in box and enter "0" in its place. I did as instructed and re-filed my returns but again received a message saying they both were rejected. I know I can print but that's not what I want to do.
Are you saying that you did not file your 2018 return at all? If that's the case and entering "0" doesn't work, then you unfortunately need to paper file.
However, if you did file your 2018 return, there are a few places you can get your 2018 AGI: