But it’s not in the same blueprint.
Heal is in BP Third Person Character
Overlap is handled in BP Actor
I’m guessing Target0 is your attempt at getting a reference to the player character by declaring a variable but it doesn’t just work like that.
In this context, you can easily reference the overlapping player by grabbing OtherActor pin from overlap event, like you already did to check actor Tag. Cast OtherActor to BP Third Person Character and use that to call its Heal function.