IRS rejected 2019 filing because they rejected my 2018 AGI. I verified the AGI on my 2018 TT filing AND on the IRS return transcript. None of the other explanations fit.

[SJP5]

I did file 2018 late, but not after mid-November.  The AGI is not rounded.
What else can I do other than mail in the return which I'd like to avoid doing?

[AnnetteB6]

Since you did file late, try entering '0'.  If it is accepted, then you're done.  If it is not, you can still mail the return.  

@SJP5