If you have registered for an account a receipt is automatically emailed to the registered email address you entered. If the payment fails you will also be emailed a notification of this.
If you have not registered for an account, during the payment process you are asked if you wish to enter an email address, but this is not mandatory. After a successful payment you will be offered the chance to print a copy of the receipt or asked again if you wish to enter an email address in order for a receipt to be sent by email