How to properly create GSM?

I'm writing my semester project and it has to be made in C++ and I'm more into other languages. I would like to create a thing that is managing my game states, but I'm not doing well. I made the same game state managing system in Java and I would like to keep the same appropach.

gsm.h

#pragma once

#include <iostream>
#include <map>

#include "gamestate.h"

class GameStateManager {
private:
    std::map<int, GameState> gameStates;
    GameState currentState;
public:
    GameStateManager();
    void method();
    void add(int id, GameState state);
};

gsm.cpp

#include "gsm.h"
#include "playstate.h"

GameStateManager::GameStateManager() {
}

void GameStateManager::add(int id, GameState state) {
    gameStates.insert(id, state);
}

void GameStateManager::method() {
    currentState.method();
}

gamestate.h

#pragma once

#include "gsm.h"

class GameState {
protected:
    GameStateManager gsm;
public:
    GameState(GameStateManager gsm);
    virtual void method();
};

gamestate.cpp

#include "gamestate.h"

GameState::GameState(GameStateManager gsm) : gsm(gsm) { }

playstate.h

#pragma once

#include "gamestate.h"

class PlayState : public GameState {
public:
    PlayState(GameStateManager gsm);
    void method() override;
};

playstate.cpp

#include "playstate.h"
#include "gamestate.h"
#include <cstdio>

PlayState::PlayState(GameStateManager gsm): GameState(gsm) {}

void PlayState::method() {
    printf("Say hello");
}

main.cpp

#include "gamestate.h"
#include "gsm.h"
#include "playstate.h"

int main() {
    GameStateManager gsm;
    PlayState playState(gsm);
    gsm.add(0, playState);
}

I got a lot of errors like: 'GameState': undeclared identifier, syntax error: indetifier 'GameState'