"Destination address required" when send message in other direction - c++

Question

I have client and server app. They use udp socket to communicate.
I can send some message from client side and receive it at server. But I can't send message in other direction.
I modify client and server boost example.
My server:
#include <cstdlib>
#include <iostream>
#include <string>
#include <boost/asio.hpp>
using boost::asio::ip::udp;
enum { max_length = 1024 };
int main(int argc, char* argv[]) {
try {
if (argc != 2) {
std::cerr << "<port>\n";
return 1;
}
boost::asio::io_context io_context;
int port = std::atoi(argv[1]);
udp::endpoint endpoint(udp::v4(), port);
udp::socket *socket = new udp::socket(io_context, endpoint);
std::cout << "starting loop\n";
while(true) {
#ifdef GOOD_RIRECTION
char data[max_length];
size_t len = socket->receive(boost::asio::buffer(data, max_length));
std::cout << "Recieved: "<< std::string(data, len) << '\n';
#else
std::cout << "Enter message: ";
char request[max_length];
std::cin.getline(request, max_length);
size_t request_length = std::strlen(request);
socket->send(boost::asio::buffer(request, request_length));
#endif
}
} catch (std::exception& e) {
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
My client:
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/asio.hpp>
using boost::asio::ip::udp;
enum { max_length = 1024 };
int main(int argc, char* argv[]) {
try {
if (argc != 3) {
std::cerr << "<host> <port>\n";
return 1;
}
boost::asio::io_context io_context;
udp::socket *socket = new udp::socket(io_context);
udp::resolver resolver(io_context);
udp::resolver::results_type endpoints = resolver.resolve(udp::v4(), argv[1], argv[2]);
socket->connect(*endpoints.begin());
std::cout << "starting loop\n";
while (true) {
#ifdef GOOD_RIRECTION
std::cout << "Enter message: ";
char request[max_length];
std::cin.getline(request, max_length);
size_t request_length = std::strlen(request);
socket->send(boost::asio::buffer(request, request_length));
#else
char data[max_length];
size_t len = socket->receive(boost::asio::buffer(data, max_length));
std::cout << "Recieved: "<< std::string(data, len) << '\n';
#endif
}
} catch (std::exception& e) {
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
where GOOD_RIRECTION is defined everything works fine.
When it is not - I got send: Destination address required exception on first send.
As far as I understand sockets are direction independent so I do something during establish connection. But I can't understand what exactly.
update:
From comments I understand that there is no "connection" in udp.
I build my client twice (with and without GOOD_RIRECTION define).I tried use one to send message and another to receive. In such situation I didn't receive first message and got send: Connection refused on sending second message.