If you want to apply cost centers, you can do so by using the billingId. You can provide a billingId with each individual order.
For instance, if you have a campaign called "Christmas" and want to itemize all costs associated with it, use "Christmas" as the billing ID for those orders. This way, your monthly invoice will include a detailed breakdown of all expenses related to the "Christmas" campaign.
Please see this JSON example on how to apply the billingId correctly.
P.S. do not use the billingId with unique strings as this will create a separate line for each indivdual order on your invoice specification.