Once an order has been shipped, Amazon may no longer allow you to cancel its fulfillment. You can submit a cancellation request through Shipr if the option is available, but Amazon determines whether the request can be accepted. If the order has already been shipped or can no longer be stopped, the cancellation request may fail.
If Amazon rejects the request, the fulfillment may continue as planned. Check the notification from Shipr and the order status in Amazon Seller Central for further details.
Please note that changing the Shopify order cancellation setting does not affect Amazon's decision to accept or reject a cancellation request.