check if damage was from fireball

Im making a bossfight that takes extra damage from fireballs that have to be redirected from the player.

The problem is that it just doesnt work, i believe the cause is that fireballs dont trigger the global trigger "entity attacked"

Ive used both source entity and immediate source entity, and ive tried pretty much every other trigger that might possibly work. and even the trigger in the entity itself.

Is there a way to do this that im just missing?