What do I do if I answered 0 but it's still rejected?

[DoninGA]

If the IRS rejected your tax return for the 2017 AGI then you will have to print and mail the tax return.

See this TurboTax support FAQ for the procedure to print and mail a tax return using the online editions - https://ttlc.intuit.com/questions/1944348-how-do-i-print-and-mail-my-return-in-turbotax-online