Using custom classes in different project as member of class C++ - ERROR

Question

I am new to C++, and I am currently working on 2 different projects within the some solution in C++ with VSC and I am encountering the error "A class-qualified name is required"; I have created a custom class in a file inside a namespace like so in project Stock:

//in file Stock.h, project Stock

#pragma once
#include "CandleStick.h"
#include "StockRecord.h"
#include "MarketQue.h"
#include <string>
#include <vector>

namespace Stock {
    class Stock {
    private:
        std::string s_stockID;
        MarketQue* s_topCur;
        StockRecord s_stockRecord;
        std::vector<CandleStick> s_candleSticks;
        unsigned int s_totalVol;
    public:
        Stock(const std::string&, MarketQue&, std::vector<unsigned int>&, unsigned int); //stockID, s_topCurPrice_B, s_topCurPrice_S, s_topCurVol_B, s_topCurVol_S, cs_interval, total_vol
        void updateStock(int);
        ~Stock();
    protected:
    };
}

//in file Stock.cpp, project Stock
#include "Stock.h"

Stock::Stock::Stock(const std::string& stockID, MarketQue& topPrices, std::vector<unsigned int>& csInterval, unsigned int totalVol)
    :s_stockID(stockID), s_topCur(&topPrices), s_stockRecord(StockRecord(topPrices.mq_size)), s_totalVol(totalVol) {
    s_candleSticks.reserve(csInterval.size());
    for (unsigned int i = 0; i < csInterval.size(); i++) {
        s_candleSticks.emplace_back(topPrices.mq_topPrice_S[0], topPrices.mq_topPrice_B[0], csInterval[i]);
    }
};

void Stock::Stock::updateStock(int totalVol) {
    s_totalVol = totalVol;
    s_stockRecord.updateStockRecord(*s_topCur);
    for (unsigned int i = 0; i < s_candleSticks.size(); i++) {
        s_candleSticks[i].updateCandleStick((s_topCur->mq_topPrice_B)[0], (s_topCur->mq_topPrice_S)[0]);
    }
}

Stock::Stock::~Stock() {};

I have successfully linked the 2 projects together (I think, tested it in the main function with a file called App.cpp in project Market):

//in file App.cpp, project Market
#include "Stock.h"
#include "MarketQue.h"
#include <string>
#include <array>
#include <vector>

int main() {
    //initializing
    const std::string stockID = "001";
    Stock::MarketQue topPrices(3);
    std::vector<float> topCurPrice_B = { 3,2,1 };
    std::vector<float> topCurPrice_S = { 4,5,6 };
    topPrices.mq_topPrice_B = topCurPrice_B;
    topPrices.mq_topPrice_S = topCurPrice_S;
    std::vector<unsigned int> topCurVol_B = { 10,11,12 };
    std::vector<unsigned int> topCurVol_S = { 13,14,15 };
    topPrices.mq_topVol_B = topCurVol_B;
    topPrices.mq_topVol_S = topCurVol_S;
    std::vector<unsigned int> cs_Interval = { 100,300,1000 };
    unsigned int totalVol= 3+2+1+4+5+6;
    Stock::Stock first_stock(stockID, topPrices, cs_Interval, totalVol);
    totalVol = 100;
    first_stock.updateStock(totalVol);
    //testing update
    topCurPrice_B = { 13,12,11 };
    topCurPrice_S = { 14,15,16 };
    topCurVol_B = { 110,111,112 };
    topCurVol_S = { 113,114,115 };
    topPrices.mq_topPrice_B = topCurPrice_B;
    topPrices.mq_topPrice_S = topCurPrice_S;
    topPrices.mq_topVol_B = topCurVol_B;
    topPrices.mq_topVol_S = topCurVol_S;
}

However, when I try to use this class(Stock::Stock) as a member inside of another class (in project Market), I received the error mentioned above ("A class qualified name is required");

I first did this:

//in file Market.h, project Market

#pragma once
#include "Stock.h"
#include <string>
#include <vector>

namespace Market {
    class Market {
    private:
        std::string marketID;
        std::vector<Stock::Stock> stock; //received error
        Stock::Stock stock;
    public:
        Market();
        void updateStock();
        ~Market();
    protected:
    };
}

At this point i figured it might be because of the namespace Market making it Market::Stock::Stock and i decided to remove the namespace Market:

//in file Market.h, in project Market

#pragma once
#include "Stock.h"
#include <string>
#include <vector>

class Market {
private:
    std::string marketID;
    std::vector<Stock::Stock> stock;
public:
    Market();
    void updateStock();
    ~Market();
protected:
};

I'd like to ask how to fix this problem, and if possible can someone explain to me what is happenning to the code that caused the error?

Thank you very much for your time.