In CRM Billing scenario, incomplete billing due list items will be generated if there are errors occured during billing due list items processing. You can use T-Code /N/BEA/CRMB04 to display the incomplete billing due list items.
Below is some back ground information shared by developer regarding to the incomplete billing due list item:
'Incomplete billing due list item exists for various reasons. Technical and customizing errors are not the only reasons. The existence of the incomplete due list item is also required by many normal business processes. In many cases, business processes also create incomplete due list items during their daily usage. There is one example which could explain that. Whenever user canceling an already invoiced sales order, CRM Billing will trigger an automatic cancellation for the corresponding billing document(s). In this process, in most enterprises, business user who has the authorization to cancel a sales order sometimes doesn’t have the authorization to cancel a billing document. The reason behind this restriction is quite obvious. These two documents belong to two different business units. Because of this restriction, the automatic cancellation may fail and incomplete due list item(s) will be created out of that. Therefore, whenever using CRM Billing, it is very important to monitor the incomplete due list item in a regular basis, and process them basing on the information which is stored in the incomplete due list item’s error log.'
In /N/BEA/CRMB04 you can use button 'Display Error log' to check the reason for each failed item.
If error log shows billing relevant customizing issues, please check and correct the customizing settings under T-Code SPRO SAP Reference IMG -> Customer Relationship Management -> Billing.
If the errors are issued during billing due list item creation or update from preceding document, you can directly correct the errors in the preceding document. The billing due list items will be updated automatically after you save the preceding document. If errors are issued during billing document creation, after correct the cause of the error, you can reprocess the incomplete billing due list items directly with T-CD /n/BEA/CRMB04.
When the error which causes the incomplete billing due list item has been corrected, you can re-process the item to generate billing document.