Why do I ask such a question? Because 300,000 is a bit high. If the other party is required to pay the litigation costs, the court will definitely ask why. And the other person is likely to say that it has nothing to do with him, and so on. , or it is wrong, or it is coerced, and so on. With these bases, you can prove to the court why the other party wrote this IOU in the first place, so that the court can support you to the maximum extent!

It's more important that you keep these things, especially what he wrote!