To cancel a Pending order:
On the left sidebar of the Orders screen, click on "Pending" then search for and click on the order you wish to cancel.
On the left slider that appears, click the 3-vertical-dot icon at the top of the page. Next, click "Cancel Order".
If you do not want to return quantity to stock "uncheck" the box that says "Return Quantity to stock" on the subsequent pop-up message.
Communicating Cancellations between Zentail and your Sales Channels
Channels that can update Zentail with a cancelled status (customer initiated cancellations).
Inventory is automatically returned to stock (since it's a cancellation and not a return).
Channels where Zentail can send a cancelled status to the channel (seller initiated cancellations).
Amazon, eBay, Facebook, Walmart and Google
Cancellations must be made on the channel for
BigCommerce, Wish, Magento, Newegg and Shopify
Note: it's still beneficial to mark these orders as cancelled in Zentail for two reasons - for your own records and because you have the option to return the units to inventory or not.
Also, a line item may not be cancelled, but product on the order may be added by adding an additional shipment or package to the order.