Using a custom fulfillment service
If you want to use a custom fulfillment service, then you need to activate it, and then you can use the service to fulfill orders.
When you mark an item or order as fulfilled from your Shopify admin, the fulfillment service is sent an email with the information they need to fulfill the order for you.
If you fulfill orders manually, then you need to open the order and mark the order or item as fulfilled.
If you fulfill orders automatically, then the order or item is automatically marked as fulfilled.
You can include tracking information and send your customers fulfillment notifications when you mark an order as fulfilled.
Cancel or change a fulfillment
If you use a custom fulfillment service, then you need to contact your fulfillment service to cancel or make changes to your fulfillment.