I had to file my 2017 taxes by mail so i did enter the correct AGI for 2017 do I need to file 2018 by mail as well

[xmasbaby0]

If you filed your 2017 return by mail in a timely manner then use that 2017 AGI on your 2018 return, and it should be okay.  If you filed late then the 2017 AGI might not be in the system.  If that is the case, then try using zero.  If neither one works then you will need to print, sign and mail 2018.

[Critter]

If you filed late or amended your return, your correct 2017 AGI may not be in the system. 

If entering the amount from your 2017 tax return does not work, then try entering “0” instead.  If that does not work and you still cannot e-file, then print, sign, and mail your tax return.

https://ttlc.intuit.com/questions/1944348-how-do-i-print-and-mail-my-return-in-turbotax-online