在Centos服务器和本地得到空白响应，它工作正常。我试图禁用Centos上的防火墙，然后再试一次，但仍然得到空白响应。

$api_key = 'api_key';
$fields = array (
'registration_ids' => array (
$device_id
),
'data' => array (
"message" => $message
)
);
$headers = array(
'Content-Type:application/json',
'Authorization:key='.$api_key
);
$url = 'https://fcm.googleapis.com/fcm/send';
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
$result = curl_exec($ch);