The IRS uses your name, Social Security number and the 2019 AGI for your electronic signature for the e-filed 2020 tax return.
If you did not file a 2019 tax return then indicate that in the File section of the program. Or you can enter a 0 (zero) for the 2019 AGI if you did not file a 2019 tax return or if the IRS has not fully processed the 2019 tax return that was filed.
The 2019 AGI is on the 2019 Federal tax return Form 1040 Line 8b.
