Are you working on a 2018 return?  There is no such thing as "short form" or "long form" now.  There is just a Form 1040 with six possible added schedules for various types of income, credits, deductions, etc.  Many state forms are not yet ready.  The IRS is not accepting federal returns until January 28 at the earliest.  If you e-file your federal return without your state return, you will have to wait for your federal return to be accepted before you can file your state return.  So you might just as well wait for MO to get its forms ready.

<a rel="nofollow" target="_blank" href="https://www.irs.gov/forms-pubs/about-form-1040">https://www.irs.gov/forms-pubs/about-form-1040</a> 

I am working on a 2018 return as well and it told me the same thing.....Missouri Resident (Long Form) wont be ready until 1/24/19.  I have one W-2. NO deductions, NO credits. NO children. Very basic and straight forward. A filing that should take literally 10-15min. Why do I need this "Long Form"??