index.php

<?php
$secretHash="xxxxxx";
$accessCode='xxxxx';
$merchantId='xxxxx';    

$data = array(
    "vpc_AccessCode" => $accessCode,
    "vpc_Amount" => '100',
    "vpc_Command" => 'pay',
    "vpc_Locale" => 'en',
    "vpc_MerchTxnRef" =>  "REF_".time(),
    "vpc_Merchant" => $merchantId,
    "vpc_OrderInfo" => "Order_N_".time(),
    "vpc_ReturnURL" => urlencode("yourReturnUrl"),
    "vpc_Version" => '1',
    'vpc_SecureHashType' => 'SHA256'    
);

ksort($data);
$hash = null;
foreach ($data as $k => $v) {
    if (in_array($k, array('vpc_SecureHash', 'vpc_SecureHashType'))) {
        continue;
    }
    if ((strlen($v) > 0) && ((substr($k, 0, 4)=="vpc_") || (substr($k, 0, 5) =="user_"))) {
        $hash .= $k . "=" . $v . "&";
    }
}
$hash = rtrim($hash, "&");

$secureHash = strtoupper(hash_hmac('SHA256', $hash, pack('H*', $secretHash)));
$paraFinale = array_merge($data, array('vpc_SecureHash' => $secureHash));
$actionurl = 'https://migs.mastercard.com.au/vpcpay?'.http_build_query($paraFinale);

//print_r($actionurl);
header("Location:".$actionurl);
?>