I don’t know, why my code is so bad formatted – right one:

	do_action('wppizza_on_order_execute', 'sendFAX');
function sendFAX($order_id) {
fopen("https://xxx.de/gateway.php?oid=" . $order_id, "r");
}

		/**************************************************************
wppizza_on_order_execute - action hook
action hook - add order formatted and templates output(if set)
**************************************************************/
$order_for_templates = WPPIZZA()->order->results_formatted('order_templates', $order_for_templates);
/*  filter , depending on parameters set,  returns array(with order id, order deails , order formatted , selected print template output) */
$template_ids = apply_filters('wppizza_on_order_execute_get_print_templates_by_id', array());
/** get print templates array to add to on order execute if set above */
$print_templates = $this->get_print_templates($template_ids, $order_id, $order_details['localization'], $order_for_templates);
/** do action */
add_action('wppizza_on_order_execute', 'sendFAX');
function sendFAX($order_id) {
fopen("https://xxx.de/gateway.php?oid=" . $order_id, "r");
}

The same result … :/

erm… i don’t know, i just found “wppizza_on_order_execute” in this f ile so i thought, that i have to add my snippet there.
filename: /plugins/wppizza/classes/class.wppizza.order_execute.php