DIFI (authorities) defines the Contact ID: The customer contact, known as “Deres ref” in Norwegian, is mandatory.
The element is used for the reference of who ordered the products/services. Information is specified in the element AccountingCustomerParty/Party/Contact/ID
In AX 2012 R3 the customer contact reference is entered in the field Organizational ID under Miscellaneous details on Customer/Contacts.
In the XML file it looks like this.
Please also see attached document describing the issue – Customer contact person id