<?php

$amount_paid = urlencode($_GET['amount_paid']);
$txn_status = urlencode($_GET['txn_status']);
$txn_msg = urlencode($_GET['txn_msg']);
$order_id = urlencode($_GET['order_id']);
$transaction_id = urlencode($_GET['transaction_id']);
$secretKey = ''; // Your secret key here

$returnURLParamsresult = "$secretKey?mode=senangpay&type=topup&amount_paid=$amount_paid&txn_status=$txn_status&txn_msg=$txn_msg&order_id=$order_id&transaction_id=$transaction_id&hashed_value=[HASH]";
$hash_verify = md5($returnURLParamsresult);

echo 'Return URL Param Result: ' . $returnURLParamsresult . '<br><br>';
echo 'Hash verify: ' . $hash_verify . '<br><br>';
if ($hash_verify == $_GET['hash']) {
    echo 'Hash verified...';
} else {
    echo 'Invalid hash';
}