How to Redirect to custompage.php instead of viewinvoice.php if payment fails in WHMCS Vs 6.2.0

[terungwa]

I wish to redirect to a custom page following the failure in payment as returned by payment gateway.
To this end, I am using the ShoppingCartCheckoutCompletePage hook to check this using the variable $vars['ispaid'].
When payment is successful, $vars['ispaid'] is true and the redirect to the thankyou page works.
 

 

add_hook('ShoppingCartCheckoutCompletePage', 1, function ($vars)
{
    # Will be true if the order has been paid
    if($vars['ispaid'] == true)
    {
        #redirect to thank you page
        header('location:'.thankYouPage);
        die;
    }
    else
    {
        header('location:'.transactionFailedPage);
        die;
    }    
}

However the else statement is not executing when payment obviously fails,
rather the viewinvoice.php page is loaded and payment status set to 'unpaid'

Am I missing something?
How can I redirect to the transaction failed page?