What is this overpayment for? If there is contact information, use it to find out why you received the overpayment. Otherwise, contact the MO Department of Revenue and find out how to return the overpayment. 

If it's a refund of your MO state income taxes and you received form 1099-G, see 

• Do I need to report the state or local refund I got last year? Is it taxable? and

• Where do I enter a 1099-G for a state or local tax refund?

I don’t know what it is for, I’m going to call on my day off and find out.