Entity despawning when looked strait at

Could anybody help me with making some code that when you look directly at a certain entity it despawns (It wouldn't despawn if it's in your peripherals). I've tried making code that does that but it always just simply despawns the entity when it's on screen...

Here's what I did for making the entity despawn when you look at it (it simply just despawns on its own...):

https://imgur.com/gallery/9sak9TP