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You can leave the Documents tab empty: in this case, the debit note itself can be used as the basis for money refund or credit (advance) for future supplies. \ 
The "Debit Note (create)" form. The Documents tab
To add the document, click the Add button.
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In the Business Activity column, select the business activities to which the documents are related.
In the Income Item column, select the item from the Income Items list to link the income from this adjustment.
Once you added all the invoices received that you wanted, you can manually distribute the note's amount among the documents by using the Debit Note Amount column. Alternatively, you can click the Distribute Amount button and select from the following options:
- Proportion to the Number of Invoices: To distribute the debit note amount among all documents evenly.
- Proportion to the Amounts of Invoices: To distribute the debit note amount proportionally to the amounts.