Interface Issue:

The interface works on 2/5 AActors that are directly derived from AActor.

Error c:\users\####\documents\unreal projects\heistgame\source\heistgame\CP_InventoryItemPickup.h(11) : error C2504: 'ICP_UseInterface': base class undefinedc:\users\####\documents\unreal projects\heistgame\source\heistgame\CP_InventoryItemPickup.h(11): error C2504: 'ICP_UseInterface': base class undefined


//////////////////////////////////////////////////////////////////////////
//                         CP_UseInterface.h                            //
//////////////////////////////////////////////////////////////////////////


#pragma once

#include "CP_Character.h"
#include "CP_UseInterface.generated.h"

UINTERFACE(NotBlueprintable)
class HEISTGAME_API UCP_UseInterface : public UInterface
{

	GENERATED_UINTERFACE_BODY()

};

class HEISTGAME_API ICP_UseInterface
{

	GENERATED_IINTERFACE_BODY()

public:

	UFUNCTION(BlueprintNativeEvent, Category = "_Heist")
		bool InterfactWith(ACP_Character *callingCharacter);

};

//////////////////////////////////////////////////////////////////////////
//                            CP_LootBag.h                              // THIS WORKS
//////////////////////////////////////////////////////////////////////////

#pragma once

#include "GameFramework/Actor.h"
#include "CP_Character.h"
#include "CP_UseInterface.h"
#include "CP_LootBag.generated.h"

UCLASS()
class HEISTGAME_API ACP_LootBag : public AActor, public ICP_UseInterface
{
	GENERATED_BODY()

public:

	ACP_LootBag();
	virtual void BeginPlay() override;
	virtual void Tick( float DeltaSeconds ) override;

	//Remove after testing confirmation and set in const
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
		float bagWeight;

	//May not need this at a later date
	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
		int32 bagValue = 2;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
		bool isHeld = false;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
		ACP_Character* lastTouchActor;

	virtual bool InterfactWith_Implementation(ACP_Character *callingCharacter) override;

};

//////////////////////////////////////////////////////////////////////////
//                            CP_LootBag.cpp                            // THIS WORKS
//////////////////////////////////////////////////////////////////////////

#include "HeistGame.h"
#include "CP_LootBag.h"

ACP_LootBag::ACP_LootBag()
{

	bagWeight = 25.f;
	PrimaryActorTick.bCanEverTick = true;

}

void ACP_LootBag::BeginPlay()
{
	Super::BeginPlay();

}

void ACP_LootBag::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );

}

bool ACP_LootBag::InterfactWith_Implementation(ACP_Character *callingCharacter)
{

	//Loot bag
	if (!callingCharacter->hasBag && !isHeld)
	{

		//Preventing this being called again
		callingCharacter->hasBag = true;
		callingCharacter->heldLootBag = this;
		isHeld = true;
		lastTouchActor = callingCharacter;

		//Set the collision and physics
		SetActorEnableCollision(false);
		Cast<UStaticMeshComponent>(GetRootComponent())->SetSimulatePhysics(false);

		//Attach the item to our socket
		const FAttachmentTransformRules attachmentRules(EAttachmentRule::SnapToTarget, true);
		AttachToComponent(callingCharacter->GetMesh(), attachmentRules, FName("BagBone"));

		return true;

	}

	return false;

}

//////////////////////////////////////////////////////////////////////////
//                      ACP_InventoryItemPickup.h                       // THIS DOES NOT WORK
//////////////////////////////////////////////////////////////////////////

#pragma once

#include "GameFramework/Actor.h"
#include "CP_UseInterface.h"
#include "CP_InventoryItemPickup.generated.h"

UCLASS()
class HEISTGAME_API ACP_InventoryItemPickup : public AActor, public ICP_UseInterface
{
	GENERATED_BODY()

public:

	ACP_InventoryItemPickup();
	virtual void BeginPlay() override;
	virtual void Tick( float DeltaSeconds ) override;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
	int32 keyID = -1;

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
	bool isLockpick = false; //if this is a lockpick main item

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
	bool isHack = false; //if this is a hack main item

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
	bool isCrowbar = false; //if this is a Crowbar main item

	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "_Heist")
	FString iconName = "Thief"; //Thief is the default

	virtual bool InterfactWith_Implementation(ACP_Character *callingCharacter) override;

};

//////////////////////////////////////////////////////////////////////////
//                      ACP_InventoryItemPickup.cpp                       // THIS DOES NOT WORK
//////////////////////////////////////////////////////////////////////////

#include "HeistGame.h"
#include "CP_InventoryItemPickup.h"

// Sets default values
ACP_InventoryItemPickup::ACP_InventoryItemPickup()
{
 	// 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;

}

// Called when the game starts or when spawned
void ACP_InventoryItemPickup::BeginPlay()
{
	Super::BeginPlay();

}

// Called every frame
void ACP_InventoryItemPickup::Tick( float DeltaTime )
{
	Super::Tick( DeltaTime );

}

bool ACP_InventoryItemPickup::InterfactWith_Implementation(ACP_Character *callingCharacter)
{

	return false;

}