You should get anyone who wants tax exempt status to send you a signed form. Here in PA the tax police don’t recognize just a tax number you must have a signed exemption form on file if they audit you. Once you get a tax exempt number just enter it in the sales tax id field in the buyers info pop up. You have to access that under orders/in process then highlight the order you want and on the right side view click the buyer info (pencil) to the right of sold to. Once you enter the # and refresh the sales tax should go away and you can resend the invoice.
