What happens in a transaction:

A transaction is created in PrestaShop, this message is sent to wallee to create a payment transaction:
When the transaction is created, the generated order ID is passed on. This ID will appear on the buyer's bank statement. Further, it will also appear in the merchant's payout report. If a payment has an error or fails, the transaction fails and a new transaction is created if the buyer is trying a second or third time to pay for their basket. 

Traceability:

By having the failed order in the PrestaShop database, this allows the merchant to directly see when a buyer tried multiple times in the backend of PrestaShop.

Order Confirmation Email: 

If the mail hook plugin is installed, this will prevent the sending of the email every time an error or a fail occurs, and only when an order/transaction actually succeeded. See: https://github.com/wallee-payment/prestashop-mailhook