Procedure:
1) Go ahead and E-File your 2019 tax return now...since your 2018 file was rejected, you use a "0" (zero) for your 2018 AGI...since the IRS didn't actually get/save your 2018 file..you use a zero.
2) For your 2018 file , you have to print it out and mail it in yourself. If you have a state to file too..you'll have to print that out and mail it in too (to your State's tax department...not the IRS). IF your file in your account is actually complete, you can save it to a PDF, print it out, and mail-file just the form 1040, and any other forms that have an attachment sequence number in the upper-rt corner of the first page (Worksheets are not filed). Don't forget to sign/date, and include any W-2 forms + any other tax forms that show tax withholding on them.
IF you didn't complete your 2018 file, or have errors to correct (or change of address since last year) then you'll have to buy/download/install the TTX Desktop software on a full MAC or Windows computer to finish off your 2018 taxes...no E-filing allowed for 2018 taxes at this late date...only print and mail by yourself.
https://turbotax.intuit.com/personal-taxes/past-years-products/
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Another FAQ:
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...
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Unless you have the original Reject code...there's no way to determine why 2018 was rejected...double check you SSN's listed to make sure they show the right person/SSN are connected (if you are married, or have dependents) . Usually, the rejection is for the SSN or the prior year AGI....(but you don't need your 2017 AGI to mail-file your 2018 file now.)
Due to the Pandemic...mail-filed tax returns may not be processed for many-many months...so don't expect fast processing. Use a tracking method at eh Post Office Service counter (Certified...or Registered mail..if they are open)...so that you have a printed record of the date you mailed them. Make sure you keep a second paper copy yourself in you own tax folder.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
