Like another comment said, there are reasons payroll companies exist, and these days there are tons of services that make this easy to do, compliantly. E.g. there is a good reason like the majority of small/medium-ish sized business I know use Gusto because they make it really easy to add contractors or employees (and I'm not specifically pitching Gusto, there are a lot of competitors you can search for). While these products aren't free, the benefit of their SaaS model is that it's a per-employee cost that can grow with you.