Following the U.S. tax law and IRS regulations, merchants must collect W-9 forms from all affiliates who are US citizens. It is a way for the government to ensure taxes are paid. Learn more about the W-9 form here: https://www.irs.gov/forms-pubs/about-form-w-9
To require your affiliates to fill out and send you the W-9 form, please enable the function by going to Settings > Payment > Tax documents, then click Set up.
On the Tax documents page, please enable Require W-9 form submission.
After that, the option to enter tax information will appear in each of the affiliates' accounts (Affiliate admin > Settings > Tax information).
After the affiliate confirms that they are a US citizen, the instructions for submitting their W-9 form will show up for them to follow:
It is required to provide the affiliate's signature and date on the W-9 form. To sign the form, open the PDF file on a PDF reader software (such as Foxit Reader, Adobe Reader, etc.) and find the PDF sign tool.
Once an affiliate has submitted the W-9 form, you'll receive an email notification that contains their W-9 form. You can also see it from the merchant's side by going to Affiliates > click on an affiliate name > View the W-9 form.