Missouri State E-filing and online pay

I live in Missouri, and I filed my taxes online.  I also chose to have the amount owed drawn out of my bank account. When I was finishing my filing, TurboTax said that I still need to mail in my voucher, even though I am paying by automatic withdrawal, and I filed online.  (I will literally just be mailing a voucher that has sensitive information on it--our SS numbers--and no payment.  All info will have already been received at the State level.)
Is this true, and why?