Add a first argument UPrimitiveComponent* in your OnHit function
In .h
UFUNCTION()
void OnHit(UPrimitiveComponent* HitComponent, AActor* OtherActor, UPrimitiveComponent* OtherComponent, FVector NormalImpulse, const FHitResult& Hit);
In .cpp:
void AFPSProjectile::OnHit(UPrimitiveComponent* HitComponent, AActor* OtherActor, UPrimitiveComponent* OtherComponent, FVector NormalImpulse, const FHitResult& Hit)
{
if (OtherActor != this && OtherComponent->IsSimulatingPhysics())
{
OtherComponent->AddImpulseAtLocation(ProjectileMovementComponent->Velocity * 100.0f, Hit.ImpactPoint);
}
}