More accurately, you have to refute the evidence that's already been produced that you do possess something. For example, if someone says "I paid tlrobinson 2

More accurately, you have to refute the evidence that's already been produced that you do possess something. For example, if someone says "I paid tlrobinson 2 bitcoins for mowing my lawn on Sunday," you could produce evidence that you were on a business trip on Sunday and therefore couldn't be the same tlrobinson referenced in the previous statement. Or argue that the person making that statement is a liar. Or point out that 2 bitcoins is an absurd amount to pay for mowing a lawn. Etc.