error occured: Invalid IP ::1

I am trying out GetClient Password on External API

<?php 
$url = "http://localhost:81/whmcs/includes/api.php"; # URL to WHMCS API file goes here
$username = "admin"; # Admin username goes here
$password = "pass"; # Admin password goes here

$postfields["username"] = $username;
$postfields["password"] = md5($password);
$postfields["action"] = "GetClientPassword";
$postfields["userid"] = "1";

$ch = curl_init(); 
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_TIMEOUT, 10);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $postfields);
$data = curl_exec($ch);
curl_close($ch);

$data = explode(";",$data);
foreach ($data AS $temp) {
	$temp = explode("=",$temp);
	$results[$temp[0]] = $temp[1];
}

if ($results["result"]=="success") {
  echo "Success<br />
<br />
";
# Result was OK!
} else {
# An error occured
echo "The following error occured: ".$results["message"];
}
?>

Getting an error

result=error;message=Invalid IP ***.***.***.***

I already adding the IP in General Setting -> Security Tabs.

PN: I am trying this in my Localhost (xampp)

What is that I am missing here?