In the meantime I found out that I forgot the values for the hidden form variables "return" and "cancel return" and fixed them. This works - but only if the one who has payed will click the "return to shop" button on the paypal page. So which advantages do I will get by using an IPN page and how does this work?
I also need the posted value for the OrderID (store cart summary in database) on the confirmation email and as the value for the hidden form variable "invoice" but I think this belongs to the ecart forum?
(sorry if there are any stupid questions)