To access this field: from the Options Configuration window, click Misc-->Change MIV Ranges-->Change Invoice # Ranges. This field works in conjunction with the field "Ending Invoice Number."
Set this field to "1" for each store, or if you already have invoices on file, set this field to a number higher than the highest invoice already on file in that store. Multistore users: Note that the system supports having the same document number in different stores.