post https://{tenant_url}/api/v1/documents/tax/generate
This endpoint allows generating a W8-BEN form or a W9 form.
Refer to the IRS information for instructions:
W-8BEN: https://www.irs.gov/forms-pubs/about-form-w-8-ben
W-9: https://www.irs.gov/forms-pubs/about-form-w-9
A document will be generated which can be signed.