If you need to cancel your Shopify order, then you need to cancel your AliExpress order and issue a refund for your Shopify order. You can only cancel AliExpress orders that aren't shipped yet by the supplier. If you've already paid for your order, then your cancellation request needs to be approved by the supplier.
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Cancel your AliExpress order
You can cancel AliExpress orders that haven't been paid for or haven't been shipped out yet. If your order has the Awaiting Payment status, then you can cancel it immediately. If your order has the Awaiting Shipment status, then you need to request the order cancelation and wait until the supplier approves or rejects your request.
Go to aliexpress.com and log into your account.
Click Account > My Orders.
Find the order that you want to cancel and then next to the order click View Detail.
Click Cancel Order, select a cancelation reason, and then click Ok.
Refund your Shopify order
When you cancel an AliExpress order you also need to cancel your Shopify order to issue a refund for your customer. Learn more about refunding an order.
From your Shopify admin, click Orders.
Click the order that you want to refund.
Select the items you want to refund, and then click Refund.