When an external catalog is configured to punchout to a marketplace solution provider, the shopping cart back to the purchase requisition document would include items from a different supplier or suppliers.  The cXML standard allows passing of the vendor identifier in the cart message (PunchOut Order Message) to have items associated with the correct vendor(s) in the ERP, and not as items from the marketplace solution provider.  

The enhancement change request is to have Dynamics 365 SCM to recognize the D365 vendor ID at the item level in the shopping cart message and update the Vendor Name in the purchase requisition document automatically. In cXML, the ERP vendor ID is passed in under SupplierID data element.