The Oil filter comes with an "O" ring and a washer. Where does the washer go? on 2012 Kia Sorento

I change the oil on the 2012 Kia Sorento but when I removed the fileter, I did not see a metal washer anywhere. However, in the box with the filter, there was an O ring and a metal washer. What is the washer for?

Asked by for the 2012 Kia Sorento
the metal washer is usually for the drain plug
Thanks! I was thinking that, but then I've never replaced a metal washer on a drain plug before and I've been changing the oil on my cars for 15 years.