Hi, I extracted this from the AP module help file.
"Document Number
The document number is the number on the invoice, debit note or credit note you received. You can add standard prefixes to each document (such as INV, NCR, NDR, INT) so they will be grouped on combined listings."
I notice the document number should be the number on the debit note which I *received*. So, back to the question, how can I issue a debit note from my company to the vendor?