did you file 2018 late (after 10/15/2019) or amend? more than a few reports of this issue. try 0 (zero) but if you amended use the AGI from the original filing.
if these don't work you'll have to paper file.
need you please, see my last question...
sitting here waiting...
If you filed the 2018 tax return late in 2019 then the IRS will not have the AGI associated with your name and Social Security number. So try entering a 0 (zero) for the 2018 AGI and e-file the tax return again.
If this is also rejected then you will have to print and mail the tax return.
See this TurboTax support FAQ for printing a tax return for mailing - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...
if you filed in April, the AGI from the 2018 return should work. if not try 0 (zero) if that doesn't work contact support but even they may not be able to help. I can not say whether it is an IRS problem or a TT problem. There have been multiple posts where OP's claim the AGI is right but still get rejected. in such situations you can only paper file
don't know your tax situation but you may be able to use IRS free file
scroll down a little bit until you see the column labeled "FILE" then the link to efile for free
if you have a state return many states are also offering something similar on their department of revenue website.