How to send multiple fields of a reference in Y2YSync

I am working on Y2YSynch project and my target type is CSV file.

I have a custom type 'MyCustomType' that has reference of product. My requirement is to generate CSV for MyCustomType that should have product code as well as product PK in addition to other fields of MyCustomType.

I have created Y2YStreamConfiguration for MyCustomType and provided Y2YColmnDefiniton for product code as well as product PK in it.

When I try to sync, the export fails with 'ambiguous attribute' exception.

It works fine if I use only one of the product attribute product code or product PK.

When I send both fields value in single attribute product(code, PK). Y2YSync works but values comes as : <product code>:<product PK>.