There's a 30% involved when Freelancers who aren't U.S. Residents are employed by some companies conducting business on U.S. soil. The form for these cases is either W-8BEN or W-8BEN-E, instead of an independent contractor's regular W-9. It's called:
Certificate of Status of Beneficial Owner for United States Tax Withholding and Reporting
What I understood on first contact with these two tax laws is the following:
W-8BEN: for individuals, non-resident U.S. aliens.
W-8BEN-E: for entities (companies) foreign to the U.S.
I found these informative articles on the subject:
Technical article on Tipalti about W-8BEN-E forms. It closes with a view on W8 automation.
A more novice-friendly on medium.com. In this article on Medium they say that they work with Tipalti.I'm not paid to endorse any of these two platforms, but I think it was worthy of mentioning this coincidence.
Official, from the U.S. Securities and Exchange Commission.
The personal takeaway, don't fret too much about this, even if you register in a freelancer telework platform that requires it, look how simplified it is in a freelancer platform, they asked me just for the information in the picture:
DISCLAIMER: this article doesn't aim at providing any kind of legal advice. It's just a record from my research that I decided to share with others.