The other module that works is Paypal IPN.

In the confirmation function of Atos, I have this line of code which in case I'm mistaken is how the order is retreived :

PHP Code:
$sips = $this->makeRequest($order->info['total'], $currency); 
whilst in Paypal, the equivalent (appears) to be this :

PHP Code:
$this->totalsum = $order->info['total']; 
They are similar but I could be off the mark.

Any ideas ?