If you make a mistake when creating a Shipping Label to Print, you have the option of voiding that label. Unless your request to void is rejected by the postal service, you should then see an immediate refund in your account. The primary reason for rejecting a void request is on labels from too far in the past.
Go to Shipments
From the merchant portal, choose Shipments from the navigation menu.
Find the Shipment
Either scroll through the list of shipments on your Shipments page or use the Unshipped Filter to find the shipment you need.
Once you have found the shipment you're looking for, press the blue Print Label button.
Void the Label
A dialog box will open, with information about the shipping label. Press the yellow Void button. If you do not see the Void button, you have not created a shipping label for this shipment.