Amazon Marketplace Web Service (MWS) will no longer be available after March 31, 2024. All MWS developers must migrate to Selling Partner API (SP-API) to avoid service disruptions. Refer to the Migration Hub for more information.
The Fulfillment Outbound Shipment API section and the Feeds API section (using the FBA Shipment Injection Fulfillment Feed and the FBA Shipment Injection Cancellation Feed) have approximately equivalent functionality in terms of submitting and cancelling Multi-Channel Fulfillment orders. The Fulfillment Outbound Shipment API section has the advantage of being real-time, however, while the Feeds API section operates asynchronously.
For more information, see What you should know about the Fulfillment Outbound Shipment API section and What you should know about the Amazon MWS Reports API section.