How did I fix the black box around sprites?

Thread tells it all.

Set the render mode to World Space Glow.

Um, no Ned. You set Render Mode to “Additive”.

Um no.
World space glow
It works better.
who is more experienced?

The Additive mode sprite on the left cuts through the lamp prop, while the World Space Glow mode sprite on the right is only rendered if nothing blocks it.

Therefor, WSG> Additive.

You just got fucking told.

One of the only places that WSG will not work, is if you want the sprite to be visible despite it being entirely enclosed inside a model. Regardless of the glow proxy geometry size, WSG works by rendering when it’s visible. Being entirely enclosed means it’s never visible, so it will never work.

Then you use additive.