Why is the sales invoice number (RBELN) available in KE24 but not KE30?
The sales invoice number is not displayed in the KE30 reports because it is a technical characteristic i.e. it is only present in the CE1XXXX table.
KE30 reports read data from the segment level tables CE4XXXX and CE3XXXX.
If you require RBELN (billing document number) to be available in KE30 then you need to create a user defined characteristic (for example WWXYZ) and map it to KOMK-BELNR in table TKEZU
Then WWXYZ should typically be filled with the billing document number.
However, SAP does not suggest customizing as this will eventually significantly impact performance.
This is because WWXYZ will need to be a segment level characteristic (in the code KEQ3) and this will result in new CO-PA (Profitability Analysis) segments getting created each time the user posts a new billing document.
Also from a management perspective, it is not useful information to know that one billing document has generated more revenue than another billing document.
It is always helpful to analyze revenues and profits based on parameters like a customer, product or region etc.