If, instead of being such a large amount, say it were twenty thousand dollars. Thinking that he had a generous benefactor, the recipient went on a shopping spre

If, instead of being such a large amount, say it were twenty thousand dollars. Thinking that he had a generous benefactor, the recipient went on a shopping spree for ten thousand. Paypal, later determines that it was an error and wants the money back. What is the law with regard to this situation? Aside: is it just me or does there appear to be a minus in from of the sum in the image?