卷曲错误 - 资源ID＃88

I am trying to execute the following curl code:

$URL = "https://app.getresponse.com/add_subscriber.htm";
$post_data = "name=ABC&email=myemail@gmail.com&campaign_token=poga1&start_day=0&";


$ch = curl_init();
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 0);
curl_setopt($ch, CURLOPT_URL, $URL);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_exec($ch);
curl_close($ch);

Running this curl gives: Resource id #88

Any clues?

    $URL = "https://app.getresponse.com/add_subscriber.htm";
    $post_data = "name=ABC&email=myemail@gmail.com&campaign_token=poga1&start_day=0&";   

    $ch = curl_init();
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 0);
    curl_setopt($ch, CURLOPT_URL, $URL);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post_data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    $response = curl_exec($ch);
    curl_close($ch);
    echo "<pre>";
    print_r($response);

The issue was you have not assign response of curl execution