2800221 - Billing Split in SAP S/4HANA CLOUD

A) Invoice split occurs, yet a combined invoice is expected.

B) A single billing document is created, however separate billing documents for each billed reference document (for example delivery) are expected.

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SAP S/4HANA CLOUD

A) Perform a split analysis to determine why billing split occurs that is, which header partners or header fields are different. For split criteria refer to SAP Note 11162.

B) In the App 'Create Billing Documents - Billing Due list Items' select 'Create separate billing document for each item of billing due list' in the billing settings.

A) & B) In General, from SAP S/4HANA CLOUD 1902, there is the possibility to exercise more granular control over how data is copied from billable reference documents to newly created billing documents.
Read the details here, in the What's New in SAP S/4HANA Cloud 1902 document in chapter 9.1.6.3 ‘Copying Control and Custom Data Transfer Routines for Billing Documents’ and here in the SAP Help documentation. 
For influenceing the billing documents creation in this regard, develop a custom data transfer logic in BAdI SD_BIL_DATA_TRANSFER in the 'Custom Fields and Logic' app.

Read the BAdI Documentation in the app 'Custom Fields and Logic', in tab 'Custom Logic', BAdI 'Custom Data Transfer for Billing Documents':

Read also the Configuration Help in Application Area: Sales, Sub Application Area: Sales Billing, Item name: 'Copying Control for Billing Documents':

SAP Help - Billing Document Split and Convergence

SAP Help - Data Transfer and Copying Requirements for Sales Documents

SAP Help - Billing Documents

SAP Fiory Apps Library - Create Billing Documents

SAP Note - 11162 - Invoice split criteria in billing document

1561427 - Billing document split

2749007 - How to Propose Pricing (Billing) Date per Document Type Based on Delivery Date in S/4HANA Cloud

2992296 - How to bill a sales order within one billing document where item category TAN and TAD are being used - SAP S/4HANA Cloud

3009009 - Unwanted billing split - SAP S/4HANA Cloud

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