Check the Primary Keys of Child Polymorphic Business Objects
Once you have created a layout for polymorphic business objects, like descriptive flexfields (DFFs) and extensible flexfields (EFFs), confirm the business object's primary key field is configured in the Business Object Field Editor for inclusion in update requests.
Primary key fields are hidden fields the add-in uses to uniquely identify business object records. Omission of the primary key field in an update request can result in an unexpected failure, such as a 404 (Row Not Found) error.
If a polymorphic business object field is marked as a primary key, its value will be cached on download and included in subsequent update requests even if the metadata indicates the field should be hidden.
To confirm that primary key fields are configured to avoid errors on upload: