If you are using ShipStation directly connected to Shopify, then your fulfillment should work with Rebuy's Post Purchase widget automatically.

If you have a connecting service between Shopify and ShipStation (e.g. NetSuite), then you may need a custom solution. Please see the following section for what orders are supposed to look like in ShipStation to check if it is functioning properly.

Orders that are On Hold in Shopify will show up in the On Hold section in ShipStation. These orders will show that they have 0 quantity. The quantity that ShipStation shows is the fulfillable quantity. It shows as 0 quantity while On Hold because none of the items in the order should be fulfilled yet (since the order may still be modified by adding post-purchase upsell item[s]).

Once the order fulfillment hold has been released, the order will move to the Awaiting Shipment tab in ShipStation. The quantity will be updated to reflect the true quantity of the order, including any post-purchase upsell item(s).

These orders will show that the quantity was updated by the selling channel (which is Shopify in this case).

If you are testing your ShipStation integration and are not seeing orders come through right away, you can manually refresh orders for your store.