So did you enter 0 for the 2018 AGI?
How to correct the AGI
https://ttlc.intuit.com/community/agi/help/where-do-i-correct-my-agi-in-turbotax-online/00/26311
If you can’t get it to efile you will have to print and mail it.
How to mail a return from the Online version
https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online/00/26258
Be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
For AGI Reject code 031
https://ttlc.intuit.com/community/rejections/help/e-file-reject-ind-031-04-or-ind-032-04-the-agi-or-self-select-pin-from-last-year-doesn-t-match-irs/00/27197
The first time you e-filed, you picked a 5 digit e-filing pin. If you remember that pin, you can use it every year after, even if you skip tax filing in some years. If you don't remember your chosen pin, you can use your adjusted gross income (AGI) from last season. If you didn't file last season, try using zero as your AGI for this season. If that does not work, you will need to print, sign and mail your tax return. Don't forget to also print, sign and mail your state tax return.