Welcome to the Community, @dgreeley.
I have some information to share that can help set up the address on the employees W4 in QuickBooks Online.
When updating the address, make sure the city, state and zip code combination given by your employee is accurate. Once verified, let’s check if the USPS database uses the same information.
You can use the USPS tool to look it up. The website has a searchable database to find the zip code of a given street address and city, or the cities that are within a given zip code.
That should do it. Let me know how it goes and we'll take it from there. I want to make sure this gets taken care of. All the best!