Depending on the methods you have chosen, Isah may split up the lines of a journal entry for sales or purchase invoices into different databases. The financial system will in that case expect the journal entries to have a debtor or creditor account in one of the databases; for the other database(s), general entries will be used.
Whenever a line is split up, Isah changes the journal entry category into a 'General' type. For sales invoices, this is category 101; for purchase invoices it is 830. You need to link a 'General' day book to these journal entry categories.