The request you got to fill out the W-9, including your social security number and stating whether you are subject to backup withholding for tax purposes, is normal for a company that is paying you a lease bonus. At the end of the year they will be required to report that payment to the IRS. They will send you a copy of the 1099 form they use to report it. If they don’t report the payment of that bonus they will be subject to a fine by the IRS, the same as you will if you fail to report receiving that bonus payment when you file your tax return.