Hello Steve,

This feature request was addressed in Payables 92A:
A unique, incrementing, invoice number can be auto-generated for invoice batch entries by using the %n code in the Invoice Number Format field on the Accounting tab in the vendor. A Next Invoice No. field has been added to enter/show the starting/current value. The number is up to 4 digits and is trimmed. Copy batch, copy entry, import and export vendor, import invoice batch and import manual check batch (cash invoices) are supported.