It's not too long ago they would ask for information faxed using company letterhead, as a form of legitimization.
The signals they use to vet customers are, again, a decade or two behind what's technologically relevant.
To which my boss replied "Wtf is letterhead?"
Personally, i'd be more comfortable with the modern approach being something more along the lines of:
You should put the token that we'll provide you with under your corporate website's page: https://<YOUR_DOMAIN>/.well-known/identity-challenge/<TOKEN>
Of course, this does almost nothing for the website being compromised, but still feels less nonsensical than using fax and using letterheads and such.
Owning a website (or a printer, or a truck, or lots of money) doesn't mean you have a business. It's about the nature and purpose of your activities with those assets (or skills).
I can add an identity token to my personal website, but that doesn't make it a business any more than putting a saddle on a zebra makes it a horse.
This ruling from the Australian Tax Office lays out pretty clearly the defining characteristics of a business [1]. It's probably a bit different in the USA, but I'm sure it's not too dissimilar.
[1] https://www.ato.gov.au/law/view/document?docid=TXR/TR20191/N...
I had PayPal ask me for exactly this (emailed rather than faxed) recently for my PayPal business account!