One of the most common problems is that we couldn't find your Shopify orders based on the order numbers/name given. By default, Fulfill Sync use order numbers(e.g 1001, 1002) to identify your orders. If the provided format of your order is for example #1001, #1002, please change your 'Recognize my order by' to 'Order Name' instead of 'Order Number'. Verify your format by 'Test Column Mapping' and perform the sync again.