The help article on this topic needs to be updated to include my situation. I received this rejection error as well, although I did file for 2018, but filed late and by paper submittal. Despite confirming that my 2018 AGI was correct by checking its IRS transcript on IRS.gov, the AGI was rejected as incorrect. I finally called TurboTax support who suggested I try 0 as my AGI (as suggested by these responses for a 2018 non-filer) which worked/IRS accepted my eFiling.
