Convert Curl in Laravel Http facade

Question

i want refactor curl method which is work with laravel Http facade and now i'm encounter some error

public function get($data)
    {
        $post_data = http_build_query($data, '', '&');
        $sign = hash_hmac('sha512', $post_data, env('INDODAX_SECRET_KEY'));

        $response = Http::withHeaders([
             'Key' => env('INDODAX_API_KEY'),
             'Sign' => $sign,
        ])->withOptions([
            'form_params' => $data,
        ])
        ->withBody('post_data', $post_data)
        ->post(config('indodax.private.endpoint'), [
            'CURLOPT_POSTFIELDS' => $post_data,
        ]);

        return $response->collect();
    }

    public static function curl($data)
    {
        $post_data = http_build_query($data, '', '&');
        $sign = hash_hmac('sha512', $post_data, env('INDODAX_SECRET_KEY'));
        $headers = ['Key:'.env('INDODAX_API_KEY'),'Sign:'.$sign];

        $curl = curl_init();

        curl_setopt_array($curl, [
            CURLOPT_HTTPHEADER => $headers,
            CURLOPT_URL => config('indodax.private.endpoint'),
            CURLOPT_POST => true,
            CURLOPT_POSTFIELDS => $data,
            CURLOPT_RETURNTRANSFER => true,
        ]);

        $response = curl_exec($curl);

        return json_decode($response, true);
    }

i think i'm missing CURLOPT_POSTFIELDS part, how to set CURLOPT_POSTFIELDS in Http facade

i'v tried with withOptions and still same reff PHP Curl proxy option in Laravel Http Facade