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

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NTT Data

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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 about this subject is almost none, and when trying to modify the data model I launch the Generate and Transfer XML transactions which launches the child job Load Extension Attributes for XML Transactions that 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.