A returnURL enables a user to go back to the merchant's website page, after a signature or a payment made with SlimPay.
What is its content ?
No information is sent with the returnURL. But, on your enquiry, we have the possibility to activate an option which adds the transaction reference within the returnURL. So, your returnURL will be : http://YOUR/RETURN/URL?order_reference=transaction-id. Then, you can do a #get-orders with this ID and retrieve the same information as the one send with notification URL.
As we said, if you want Slimpay to send you information, you have to set up a notification URL but it has to be in HTTPS and have a SSLcertificate dedicated.