You seem to be casting to BP_FirstPersonCharacter1 on overlap are you sure that is your character?
Seems like a duplicate of BP_FirstPersonCahracter. It would be better to have your player character have an actor tag for example “Player” and then check if the other actor has the tag instead of casting.
Make sure that the sphere collider has generate overlap events ticked.
The sphere collider needs to be the first element in the hierarchy for it to register if you are using projectile movement component.