In Unreal 4.24 the overlap events must be declared as UFUNCTION methods. Otherwise the engine will crash when you start play. This is explained after the challenge slide, but FYI for anyone trying to work it out first.
UFUNCTION()
void ActorBeginOverlap(AActor* OverlappedActor, AActor* OtherActor);
UFUNCTION()
void ActorEndOverlap(AActor* OverlappedActor, AActor* OtherActor);