Unfortunately, the MWS API (the system Amazon allows 3rd parties to communicate with them through) has not been updated to handle combining commingled inventory with seller labeled inventory. For more information on this topic please see- What are the Amazon MWS Limitations?
The good news is, to bypass this limitation, you can create and upload an inbound shipping plan to Seller Central for the items listed through Stratify by following the steps below!
To begin, you will need to add the items to a Private batch.
After everything that needs to be shipped has been added, click the Review Batch button at the bottom of the List & Prep page.
On the Review Batch page, click Submit. This will bring up a window that gives you an option to send your product listing feeds, or send feeds and request proposed FBA shipment plans.
When the window appears, uncheck the box for the Request proposed FBA shipment plans from Amazon option, then click Sync. This will close your batch and allow you to begin the process of uploading the shipping plan into Seller Central.
From here, go to List>Closed Batches:
Click the name of the batch you need a Shipping Plan File for:
Click on Export and choose Shipping Plan File. This will give you a properly formatted .txt file:
- Note: You must wait 5 to 10 minutes for your feeds to fully send your listings over to Amazon prior to uploading your Inbound Shipping Plan into Seller Central. If you attempt the upload too early, Amazon will give an "Unknown SKU. The SKU for this product is unknown or cannot be found." error.
Now, you're ready to upload! Simply visit this link (click here) and upload the file.
For help with uploading the file to Seller Central, please reference the remaining steps here- Create an Inbound Shipping Plan