@bigherm8h
The mandatory withholding rate used to be 25%. I suspect (I did not verify this) that when the tax reform act of 2017 reduced the marginal tax rates, the IRS reduced the mandatory withholding amount to 24% at the same time. (The tax rate that most middle-class taxpayers pay was reduced from 25% to 22% or 24%.) If the organization‘s accountant is not up to speed and withheld extra money, that just means that you are giving the IRS a small interest free loan until tax season. It does not change the tax that you will eventually owe on the prize, and whatever amount was withheld is credited to you on your tax return.
