需要从URL接收JSON回调并在PHP中处理它

Question

我正在使用一个支付网关，该网关在完成付款后会通过URL发送JSON文件到我的网站，特别是一个PHP文件。我已将PHP文件编码如下：

$json = file_get_contents('php://input');
$obj = json_decode($json, TRUE);

if ($obj) {
    $to = 'test@test.co.uk';
    $subject = "It exists";
    $message .= $smart_id. "\r\n\r\n";
    $message .= $bbct_id. "\r\n\r\n";
    mail( $to, $subject, $message); 
} else {
    $to = 'test@test.co.uk';
    $subject = "Nothing here";
    $message .= $smart_id. "\r\n\r\n";
    $message .= $bbct_id. "\r\n\r\n";
    mail( $to, $subject, $message); 
}