1) It has to be the number from the very FIRST E-filed tax return hat was submitted and accepted, not any amended tax returns you might have done.
2) If you filed late, on paper for 2018, try a zero for the 2018 AGI.
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in the end, if you can't get it to work, you my have to print and file on paper, byt taking it to mail in at the Post office this year.