The Online service is completely shut down for 2018 taxes and is shifting the software over to 2019.
You will have to buy and download the desktop software to a full MAC or Windows computer to complete it. You can also download your .tax2018 datafile to that full computer version to complete and "Snail Mail" your finished Federal tax forms to the IRS, and state tax forms to your state. No e-filing allowed at this late date.
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-...
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
