Illinois Department of Revenue publication 102 page 3 states:

• “You may subtract tax-exempt military pay that is in your AGI, including
• Pay for duty in the armed forces, including basic training,
• Pay for duty as a cadet at the U.S. Military, Air Force, and Coast Guard academies, as a midshipman at the U.S. Naval Academy, or in ROTC, and
• Pay for duty for serving in the U.S. Armed Forces Reserves or a National Guard unit, including a National Guard unit of another state.”

Down the left side of the screen, under My Info, did you click Yes, I am a member or former member of the US Armed Forces?

Is your military pay included in your Federal Adjusted Gross Income or was it already excluded?