You can use the same document type for all billing documents. However, SAP recommends that you use different document types for real billing documents and for simulated billing documents.
If you reverse billing documents, you can assign a separate document type for the reversal document. However, you can also use the same document type for the reversal document as for the reversed billing document.
Activities
Example
You are transferring billing documents from two different external systems. For each external system, you define a document type for real and for simulated billing documents. You use different number ranges for different document types. This enables you to recognize the origin of the billing documents from the number range interval in the SAP system.