To manage the failed order:

1. Go to Prestashop Admin Panel
2. On the left navigation bar, place the cursor on OnBuy Integration and you will see it getting expanded as below:
   
   
3. Click on OnBuy Failed Orders.
   The tab appears as shown below:
   
4. Now, this can be done both in bulk or by canceling a particular failed order.
5. To cancel an individual order, click on the Cancel button in the last column of each failed order.
6. To cancel the failed orders in bulk, select all the orders and then click on the bulk actions button and from here you may click on cancel order.
7. All selected failed orders will be canceled.