Consistently getting a status of 0 even though if I copy and paste the url sent into my browser, I get a json object right back

<?php


$mainUrl = "https://api.xxxx.com/?";
$co = "xxxxx";
$pa = "xxxx";
$par = "xxxx";
$part= "xxxx";
$partn = "xxxx";
$us= "xxx";
$fields_string;
$fields = array(
            'co'=>urlencode($co),
            'pa'=>urlencode($pa),
            'par'=>urlencode($par),
            'part'=>urlencode($part),
            'partn'=>urlencode($partn),
            'us'=>urlencode($us)
            );

foreach($fields as $key=>$value) { $fields_string .= $key . '=' . $value . '&' ;}

$fields_string = rtrim($fields_string, "&");
$fields_string = "?" . $fields_string;

$url = "https://api.xxxxx.com/" . $fields_string;

$request =  $url; 

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_TIMEOUT,'3');
$content = trim(curl_exec($ch));
$http_status = curl_getinfo($ch, CURLINFO_HTTP_CODE);

curl_close($ch);
print $url;
print $http_status;
print $content; 



?>