Let's say a customer has just bought three of your listings on Back Market whose the SKU are sku_1, sku_2, and sku_3.
In your Back Office, go to 'Orders', or use directly this link.
On this page, you will see all your orders (not yet processed and processed) classed from the most recent to the older.
'Paid' means that the payment process has been checked and validated.
You can see that the order contains 3 orderlines: one for each listing. You can validate or cancel each orderline.
Let's say you forgot to update your stock and you have no more sku_3. You have to cancel the corresponding orderline. A windows displays when you click on 'Cancel'.
After you cancel the orderline, the customer will be refunded.
Once all the orderlines are validated or canceled, the order passes in the state 'Awaiting shipment'.
Even if you accepted an orderline, you can cancel it afterward by clicking on 'Reimburse'. The customer will be refunded for this orderline.
You have now to deliver the package to the shipping company. Once it's done, click on the button 'Send'. A window displays where you have to enter the shipping company, the tracking number and the tracking URL of the order.
Note that there is only one button 'Ship' for the whole order since all orderlines are gathered in the same package.
Once you fill in all the fields of the delivery information window, your order is processed.