该问题是由于API请求中timestamp参数为空导致的。可以通过使用Libcurl c++的代码示例来解决如下：

#include 
#include 
#include 
#include 

std::string bybitApiSignature(const std::string& secret, const std::string& verb, const std::string& url, const int64_t& expires, const std::string& body) {
    std::stringstream prehash;
    prehash << verb << url << expires << body;
    const std::string message = prehash.str();

    std::vector result(HMAC_SHA256_DIGEST_LENGTH);
    HMAC_SHA256(result.data(), secret.c_str(), secret.size(), message.c_str(), message.size());

    return base64_encode(result.data(), result.size());
}

int main() {
    CURL* curl;
    CURLcode res;

    curl_global_init(CURL_GLOBAL_DEFAULT);

    curl = curl_easy_init();

    std::string verb = "GET";
    std::string endpoint = "/open-api/order/list";
    std::string params = "limit=10&order_status=New";
    const int64_t expires = get_current_timestamp() + 10;
    const std::string body = "";

    std::stringstream ss;
    ss << "https://api.bybit.com" << endpoint << "?api_key=" << apikey << "&" << params
        << "×tamp=" << expires << "&sign=" << bybitApiSignature(secret, verb, endpoint, expires, body);

    std::string url = ss.str();

    if (curl) {
        curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, "GET");
        curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_callback);
        curl_easy_perform(curl);
        curl_easy_cleanup(curl);
    }

    curl_global_cleanup();
    return 0;
}

其中，需要注意对timestamp参数进行正确的传递。