Hi Marian,
In standard SD process it's not possible to raise an invoice without a reference document user can raise an invoice either with reference to sales order or delivery.
Otherwise use the T.code FB70, user can post credit or debit memo. This is normally done by FI users.
Another way to achieve is through the following steps:
- T.code SE37
- Enter - BAPI_BILLINGDOC_CREATEMULTIPLE & Execute (F8)
- Then double click on field "BILLINGDATAIN"
- Next screen, enter sales organization, distribution channel, division, order type etc., and then press F3
- In the next screen click the execute button or press F8
- Then press success
Regards,
Sharan