Hope you get this sorted out. If TurboTax had actually been using 2017 forms for 2018 returns when you used the online software, we would have seen plenty of other users who had the same issue. It is possible that you used the wrong desktop software and used 2017 software on your own computer to enter 2018 income---did you use desktop? When you look at your federal return for 2018 what forms were used?
There is simply nothing believable about TurboTax telling you that they will charge you $900 to fix this. TurboTax does not even have a service to "fix" old returns. TurboTax experts do not help with or work on past year tax returns.
If you need to file a 2018 MO return, then you could get the forms from the state and complete a correct 2018 state return by hand. Or you could seek local paid tax help with this.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/state-taxes/contact-state-department-rev...
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
