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Maintaining Billing Due Lists 
The billing due list is
the object in CRM Billing which receives the transferred billing-relevant data
from CRM Business Transactions. During input processing CRM
Billing supplements the transaction data with Customizing data and master
data, checks it and saves it in the form of a billing due list
item.
The data of the billing due list item, along with the corresponding
Customizing and master data, is the basis for the subsequent sub-process of billing. This
means that during creation of a billing document, CRM Billing does not receive
any new data from CRM Business Transactions.
CRM Billing differs from SD
Billing through the existence of the billing due list:
· In SD Billing, the billing index simply creates a reference to the order or delivery data to be billed by saving the order or delivery number.
· The aim of the billing due list concept in CRM Billing is to integrate billing-relevant data from different source applications (for example, from mySAP CRM and non-SAP source applications).