Kansas trying to make my civilian spouse pay state income taxes.

I just received a letter from Kansas saying I owe a few hundred dollars in taxes and have 15 days from the date on the letter (which was 13 days ago) to pay it or they will take legal action against me.

So our situation, I am active duty military working in Washington state but am a resident of Kansas meaning I pay my income taxes to Kansas. My wife is a Missouri resident and lives and works in Washington. She has never lived or worked in Kansas so as far as I'm concerned she shouldn't have to file a tax return in Kansas. We've been in Washington for three years now and each year we've filed jointly and removed her income from the Kansas return so her income wouldn't be included in the state taxes for a state she doesn't work or live in. Up until now there hasn't been an issue with filing taxes this way.

Does anyone know about Kansas state taxes enough to know if I'm in the right or Kansas is? I tried to reach out to them as soon as I got the letter but due to the different time zone they are currently closed. I only have tomorrow left to get in contact with them before they take legal action.