Backup withholding is a 24% federal tax a US payer withholds and sends to the IRS instead of paying you in full, when your TIN is missing or incorrect on a W-9, or the IRS flags an issue. It applies to Form W-9, which only US persons (citizens, green-card holders, and US tax residents) complete.
If you're a non-US person working entirely outside the United States, backup withholding generally doesn't apply to you. That income is generally foreign-source, and a valid W-8BEN (individuals) or W-8BEN-E (foreign companies) documents your foreign status so payments are generally exempt from Form 1099 and backup withholding.
Two exceptions to know: if any portion of your work happens physically inside the US, that portion may be subject to 30% withholding, possibly reduced by a tax treaty, separate from backup withholding. And if we don't have a valid W-8 on file before paying you, IRS presumption rules can force us to withhold anyway. Submit your form on time to avoid this.
This is general information, not tax advice. Consult a tax professional for your specific situation.
Regardless of where you're based, you need a completed tax form before you can receive payments. Complete it under Identity & Payments at app.humansignal.com.