I don’t know where you live but here in california you go to city hall and apply for a business license. It’s about 70.00 if I remember right. If your name is not in your business then you also need to file a ficticious business name. You have to run an ad in a local newspaper stating who you are and the name of your business.
It’s really pretty simple.

When I lived in Wisconsin and did that (admittedly, that was nearly 20 years ago) I simply registered with the state for a sales tax number, and that seemed to suit anyone who wanted to see proof that I was in business.

It depends on what your local zoning requirements are. In the small, incorporated City where I live there are different requirements for a business that will have clients coming to the house, as opposed to ones that does not. We are also subject to zoning requirements from the County and State.

Once you determine that you meet the various requirements, filing the paper work is the easy part.

I think the zoning requirements will only apply if you will have customers parking around your home (you’ll need parking lots) or if you will have employees (you’ll need an indoor bathroom instead of the outhouse you’re using now you know! Or, seriously, they might require a handicap accessible BR if you have employees….)

Other than that, it’s basically a way for the IRS to keep track of who’s running a business so they can keep track of who should be paying taxes.

In WA, a $25 license would work. There is an online application form. You can get it (the tax number, UBI) right after you pay. To get EUI for federal, you will need to do more filing.