Why can garbage get into a variable?

Question

C++ / C#

I have a small DLL in C++11, it clings to the WS server and waits for data and then closes the connection.
On first start everything works great. The API key comes as expected, but on the second iteration, the API key gets the contents of the error array, I can’t understand why this happens, can anyone tell me what could be the reason?

#include "stdafx.h"
#include "Project2.h"
#include "Header1.h"
//#include <eh.h>

#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>
#include <boost/asio/connect.hpp>
#include <boost/asio/ip/tcp.hpp>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cstring>

namespace beast = boost::beast;         // from <boost/beast.hpp>
namespace http = beast::http;           // from <boost/beast/http.hpp>
namespace websocket = beast::websocket; // from <boost/beast/websocket.hpp>
namespace net = boost::asio;            // from <boost/asio.hpp>
using tcp = boost::asio::ip::tcp;       // from <boost/asio/ip/tcp.hpp>

auto decorator_with_key(boost::beast::string_view& key) {
    return [key](websocket::request_type& req) {
        req.set("Api-Key", key);
    };
}

PROJECT2_API bool readSignal(char* buf, char* key_input, char* error) {
    try
    {
        boost::beast::string_view key = std::string(key_input);
        std::string host = "example.com";
        auto const  port = "3001";
        beast::flat_buffer buffer;
        net::io_context ioc;
        tcp::resolver resolver{ ioc };
        websocket::stream<tcp::socket> ws{ ioc };
        auto const results = resolver.resolve(host, port);
        auto ep = net::connect(ws.next_layer(), results);
        host += ':' + std::to_string(ep.port());
        ws.set_option(websocket::stream_base::decorator(decorator_with_key(key)));
        ws.handshake(host, "/");
        ws.read(buffer);
        ws.close(websocket::close_code::normal);
        std::string read_buffer = beast::buffers_to_string(buffer.data());
        strcpy_s(buf, 255, read_buffer.c_str());
        return true;
    }
    catch (std::exception const& e)
    {
        strcpy_s(error, 255, e.what());
        return false;
    }
    return false;
}