<?php

 $url = "http://wehost4you.dk/includes/api.php"; # URL to WHMCS API file
 $username = "username"; # Admin username goes here
 $password = "password"; # Admin password goes here

 $postfields["username"] = $username;
 $postfields["password"] = md5($password);
 $postfields["action"] = "addinvoicepayment"; #action performed by the [[API:Functions]]
 $postfields["invoiceid"] = "1";
 $postfields["transid"] = "5555";
 $postfields["gateway"] = "PayPal";

 $ch = curl_init();
 curl_setopt($ch, CURLOPT_URL, $url);
 curl_setopt($ch, CURLOPT_POST, 1);
 curl_setopt($ch, CURLOPT_TIMEOUT, 100);
 curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
 curl_setopt($ch, CURLOPT_POSTFIELDS, $postfields);
 $data = curl_exec($ch);
 $info  =   curl_getinfo( $ch );
 curl_close($ch);

 $data = explode(";",$data);

 echo '<pre>'
    . print_r( $data, 1 )
    . print_r( $info, 1 );


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

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

 ?>