My husband's W-2 has WA in box 15, but no EIN; plus an amount slightly more than his total in box 3 shown in box 16. WA state does not have income tax, so I'm confused.

He did have some Paid Family and Medical Leave, but the state says they do not provide a 1099-G for medical leaves. I don't understand what the amount in Box 16 is for? Should I just omit it since WA has no state income tax?