public static function sendPost($url, array $data, $client_ip = '')
    {
        $ch = curl_init();

        $params = http_build_query($data);

        $opt = [ 
            CURLOPT_URL => $url,
            CURLOPT_POST => 1,
            CURLOPT_POSTFIELDS => $params,
            CURLOPT_RETURNTRANSFER => 1,
        ];

        if ($client_ip) {
            $opt[CURLOPT_HTTPHEADER] = [ 
                "CLIENT-IP: {$client_ip}", "X-FORWARDED-FOR: {$client_ip}"
            ];
        }

        curl_setopt_array($ch, $opt);

        $json = curl_exec($ch);

        return $json; 
    }