My 2018 e-file was rejected because of 2017 AGI. I didn't think my 2018 return even contained that. What should I do? I would prefer not to file a paper return.

After you click e-file, there should've been a box that asked for your 2017 AGI. This is used by the IRS to confirm your identity. If it does not match what the IRS has on file, they will reject your return.

If you have a copy of your tax return from last year, look through that for your AGI. You should be able to e-file again once you have that information.