wspsc_my_custom_ipn_tasks

I’m trying to use this function:

add_action(‘wpspc_paypal_ipn_processed’, ‘wspsc_my_custom_ipn_tasks’);

function wspsc_my_custom_ipn_tasks($ipn_data) {
$firstname = $ipn_data[‘first_name’];
$lastname = $ipn_data[‘last_name’];
$email = $ipn_data[‘payer_email’];
$item_sold = $ipn_data[‘payment_status’];
//Do something with the data
return $item_sold;
}

However when I call this function in a template (the thank you page) I receive the following warning and notice:

Warning: Missing argument 1 for wspsc_my_custom_ipn_tasks(), called in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\completed.php on line 21 and defined in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\functions.php on line 537

Notice: Undefined variable: ipn_data in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\functions.php on line 538

Notice: Undefined variable: ipn_data in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\functions.php on line 539

Notice: Undefined variable: ipn_data in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\functions.php on line 540

Notice: Undefined variable: ipn_data in C:\Users\Michiel Starrenburg\Documents\My Web Sites\naturelartbyroger\wp-content\themes\naturalartbyroger\functions.php on line 541