Thank you. I did an experiment using a sample project. The payment function works fine. However, there are several problems.
1. If you press ESC without canceling on the payment page, the game will stop. If you don't restart, you can't do anything. After about 40 seconds, you will be able to move your character, but you will not be able to open the payment page again. Even if I turn the game off and on again, the payment page won't open.
2. Why is 'Enable Steam Purchase' in the plugin parameter 'False'? Shouldn't it be 'True'? The payment works regardless of true or false.
I don't know anything about coding or programming, but according to Steamworks Documentation, I need to reset the API that I exchange with the Steam serverOr maybe something like that? I think it's because the server misunderstood that the payment was continuously in progress.