How to add custom XML tag to "Load Extension Attributes for XML Transactions" BIP data model?

Summary:

Hi community,

I need to add the DUNS code to the Invoice Outbound for PEPPOL message. As per documentation, this could be added by using Load Extension Attributes for XML Transactions BIP data model.

The documentation on this subject is almost nonexistent, and when trying to modify the data model, I launch the Generate and Transfer XML transactions, which in turn launch the child job Load Extension Attributes for XML Transactions, which eventually ends in error.

I need to add the DUNS code, located at the Customer/Provider header so it shows up in the transformed Invoice Outbound CMK Message.