HISM setup in c++


I am trying to set up a grid where players can break blocks kinda like Bomberman. For the mesh, I am using a HISM and using the “remove instance” function to get rid of each block when the player attacks it. Everything works great in blueprints but when I try to change it to c++ everything breaks.

Here is the code that I am using (.h)

        #pragma once
        #include "CoreMinimal.h"
        #include "GameFramework/Actor.h"
        #include "Grid.generated.h"
        class UHierarchicalInstancedStaticMeshComponent;
        class GLEEF_API AGrid : public AActor
        	// Sets default values for this actor's properties
        	// Called when the game starts or when spawned
        	virtual void BeginPlay() override;
        	UPROPERTY(EditDefaultsOnly, Category = "Mesh")
        	UHierarchicalInstancedStaticMeshComponent* BlocksHISM ;

 #include "Grid.h"
    #include "Components/HierarchicalInstancedStaticMeshComponent.h"
    // Sets default values
     	// Set this actor to call Tick() every frame.  You can turn this off to improve performance if you don't need it.
    	//PrimaryActorTick.bCanEverTick = true;
    	BlocksHISM = CreateDefaultSubobject<UHierarchicalInstancedStaticMeshComponent>(TEXT("HierarchicalInstancedStaticMeshComp"));

First, I tried to do everything in c++ but nothing worked at all. Now, I am trying to just create a HISM in c++ and use the contrusction script in blueprints to create a grid but that breaks and does really weird things. Is there something I have to setup in c++ that is done in blueprints for me?

Thank you.

Sorry for the formatting for the code, I keep trying to change it but it keeps giving me errors