unable to print Vector data

Question

#include <iostream>
#include <array>
#include <vector>
using namespace std;

constexpr std::size_t Count{5U};

constexpr std::uint8_t Set{0x00U};
constexpr std::uint8_t Unset{0x01U};

constexpr std::uint8_t First{0x01U};
constexpr std::uint8_t Second{0x03U};
constexpr std::uint8_t Third{0x05U};
constexpr std::uint8_t Fourth{0x1DU};
constexpr std::uint8_t Fifth{0x27U};


constexpr std::array<std::pair<std::uint8_t, std::uint8_t>, Count> buffer{
    std::make_pair(First, Set), std::make_pair(Second, Unset),
    std::make_pair(Third, Unset), std::make_pair(Fourth, Unset),
    std::make_pair(Fifth, Unset)};

int main()
{
    cout<<"Hello World"<<endl;
    
    std::vector<std::uint8_t> reply;
    std::vector<std::uint8_t>::iterator it;
    
    cout<<"reply size is "<<reply.size()<<" and capacity is "<<reply.capacity()<<endl;
    reply.clear();
    reply.reserve(1U + (Count * 2U));
    cout<<"reply size after reserve is "<<reply.size()<<" and capacity is "<<reply.capacity()<<endl;

    reply.push_back(static_cast<std::uint8_t>(Count));
    cout<<"reply size after resize is "<<reply.size()<<endl;
    
    cout<<"data is "<<reply.at(0)<<reply[0]<<reply.front()<<endl;

    for (std::size_t i{0U}; i < Count; ++i) {
        reply.push_back(buffer.at(i).first);
        reply.push_back(buffer.at(i).second);
    }
    cout<<"reply size after reserve is "<<reply.size()<<" and capacity is "<<reply.capacity()<<endl;
    
    for(auto i: reply)
        cout<<"data xx : "<<i;
    
    return 0;
}

In the above snippet i am unable to print the contents of the vector at lines

cout<<"data is "<<reply.at(0)<<reply[0]<<reply.front()<<endl;

and

for(auto i: reply)
    cout<<"data xx : "<<i;

What is the reason or error in my snippet?