Here is the text from the official IRS form W-9:
Under penalties of perjury, I certify that:
The number shown on this form is my correct taxpayer identification number (or I am waiting for a number to be issued to me); and
I am not subject to backup withholding because: (a) I am exempt from backup withholding, or (b) I have not been notified by the
Internal Revenue Service (IRS) that I am subject to backup withholding
as a result of a failure to report all interest or dividends, or (c)
the IRS has notified me that I am no longer subject to backup
I am a U.S. citizen or other U.S. person (defined below); and
The FATCA code(s) entered on this form (if any) indicating that I am exempt from FATCA reporting is correct.
I don't think you are exempt from backup withholding (2a). You can see on page 3: "Generally, individuals (including sole proprietors) are not exempt from backup withholding."
Rather, you are not subject to backup withholding, because the IRS has never told you that you are subject to it (2b).
(Unless of course they have told you that you are subject to backup withholding, but if that were the case I assume you would already know about it.)