We cannot see your state return so cannot answer. The typical reason is not having enough state tax withheld from your paycheck. When the tax law changed, employers changed the amounts being wihheld from federal pay, and many also withheld less from state taxes, Compare your W-2 from 2017 to your 2018 W-2--look in box 17 and see if less was withheld for 2018. There could be other reasons as well, but that is a starting point.