Enviar JSON via POST na mesma página com PHP? API Mercado Pago

include 'system.php';

header("Content-Type: application/json; charset=utf-8");

$str_data = '
		{
		"items": [
			{
				"id": "001",
				"title": "Compra no site '.$title.'",
				"currency_id": "BRL",
				"picture_url": "https://www.mercadopago.com/org-img/MP3/home/logomp3.gif",
				"description": "Descrição",
				"category_id": "Categoria",
				"quantity": 1,
				"unit_price": 100.00
			}
		],
		"back_urls": {
			"success": "https://www.success.com",
			"failure": "http://www.failure.com",
			"pending": "http://www.pending.com"
		},
		"auto_return": "approved",
		"notification_url": "https://www.your-site.com/ipn",
		"external_reference": "Reference_1234",
	}
	';

$url ="https://api.mercadolibre.com/checkout/preferences?access_token=meutoken";
 
//Initiate cURL.
$ch = curl_init($url);
 
//Tell cURL that we want to send a POST request.
curl_setopt($ch, CURLOPT_POST, 1);
 
//Attach our encoded JSON string to the POST fields.
curl_setopt($ch, CURLOPT_POSTFIELDS, $str_data);
 
//Set the content type to application/json
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json')); 
 
//Execute the request
// $result = curl_exec($ch);

var_dump(curl_exec($ch));

include 'system.php';

$json_file = file_get_contents("http://www.mlvendas.esy.es/fin.php");

$json_str = json_decode($json_file, true);

var_dump($json_str);

echo "<br><br>".$json_str['items']['0']['id']."<br><br>";
echo "<br><br>".$json_str['items']['0']['title']."<br><br>";
echo "<br><br>".moeda($json_str['items']['0']['unit_price'])."<br><br>";
echo $json_str['init_point']."<br><br>";