I want to get the login information when completed

[Wpspc_paypal_ipn_processed]
In the hook function
Login information
I want to get
Is there a way?

add_action('wpspc_paypal_ipn_processed', 'wspsc_my_custom_ipn_tasks');
function wspsc_my_custom_ipn_tasks($ipn_data){

	$file = get_template_directory() .'/log.txt';

	$user = wp_get_current_user();
	$user_id = $user->get('ID');

	ob_start();
	var_dump($user_id);
	$result = ob_get_contents();
	ob_end_clean();

	file_put_contents($file, $result);
}

In can not be acquired

https://wordpress.org/plugins/wordpress-simple-paypal-shopping-cart/