Which field must exist for the copying control between a sales document and a billing document?

For the copying control between a sales document and a billing document in SAP S/4HANA, the existence of the document type is essential. The document type serves as a critical identifier that defines the nature of the document, such as whether it is a sales order, delivery, or billing invoice.

The document type not only helps in categorizing the documents but also determines the behavior of the documents during the copying process. It defines how data is copied from one document to another and what rules apply to this process. For instance, different document types have different settings regarding how item details, pricing, and conditions are transferred from the sales document to the billing document.

While the billing block, item category group, and reference number might play roles in the overall sales and billing process, they do not serve as the primary means of facilitating the copying control between a sales document and a billing document. In summary, the document type is a foundational element required for effective copying control in SAP S/4HANA sales processes.