You may find this website useful:
https://dor.mo.gov/taxation/individual/tax-types/income/notices.html
Note that you can email the MO tax department at income@dor.mo.gov
Also note that the website says that you can file a protest after you receive an "Assessment of Unpaid Tax Notice". The mailing address for protest letters is in that section of the website.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
