reward video have problem on X button after add listener code

[kotran88]

after add below code, after see reward video all and press X button on top right screen.
but it's not working. also, I can't install app on reward video.

document.addEventListener(this.admobFree.events.REWARD_VIDEO_REWARD, (result) => {
window.alert("reward seen")
});

how can I detect user view all video except for above code.