For customers who have sent non-Amazon orders to Amazon for fulfillment, the "Sync Fulfillment Status" button on the SHIPMENT HISTORY page will trigger a sync with Amazon. This will generate an update on the status of the shipment.
This is available for FBA orders only, so you will only see this button if that your account is enable for Amazon.
How to: Send an order to FBA
Can I run reports on Fulfillment by Amazon orders?
What is Inventory Management?
How to: Enable Amazon Multi-Channel Fulfillment
Why don't my Fulfillment by Amazon orders sync with ShippingEasy?