When orders get combined and shipped in Shipstation the 'mergedIds' from the Advanced Options should be available when querying the List Shipments endpoint. It is currently included in the orders endpoint however it is pretty much useless as one would never use that endpoint for updating orders/fulfillments in a 3rd party system like an ERP but rather they would query the shipments endpoint to check for orders that have been shipped.
As it is right now when we combine orders in Shipstation we have no way of updating our internal system and marking both orders as shipped, it will only update the master order ID.
I just came across this issue and had to basically manually process 50 orders in our ERP system because we were unaware this was how the system was set up. Not being able to find the connected orders means we are basically unable to make merged shipments, as it saves us no time, rendering the feature useless to us. Having the merge id in the return is also basically useless, as we cant do anything with it. If we could search shipments/orders by merge id we could get the orders back, or if we could at least still find the original orders we would be able to process them.
@jdevlin When we sync the fulfillment record to Shipstation we return the Shipstation Order ID and save it into our ERP fulfillment record. If they would only return the Order ID in the mergedIds we could then update both fulfillment records if they get merged inside Shipstation without searching again. Hope to see improvements to their API.
I've got the same problem. According to the documentation mergedIds is an array of Order IDs. But they're not our Order IDs, they're ShipStation's Order IDs that they autogenerate. Our order numbers get put in the "orderKey" field. You try looking up the one of the mergedIds though and nothing comes up.