Are you trying to file 2019? If you didn't file 2018 then enter 0 for the AGI to efile 2019.
Did the IRS send you a letter in the mail saying you didn't file 2018? Or how did you find out? Did you have a refund you never got?
Maybe you didn't finish filing it or it Rejected. When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. what does it say?
