SubTotal version: 1.5.58
Operating system: macOS 12.7
Device model: iMac 27" (2016)
If some of your customers are (European branches of) big U.S. corporations, chances are they require a PO or Order number (PO stands for Purchase Order) which is unique to each specific order and serves for quick identification of this order within the corporation (whereas the invoice number is unique to the supplier but not necessarily to the customer).
The textual format is always "PO {1+ digits}" and the XML field for this number (digits only) is BT-13.
While BT-13 is not required legally for e-invoices, it is required by many U.S. corporations making SubTotal de facto unusable in this case unless BT-13 is added.
Semantically, the PO number belongs to the invoice number and should be located next to it. This would require either a specific PO text field or a generic text field from which the PO can be extracted – either text field would have to be located next to the invoice number, date etc. (cf. Feature Request Additional text next to Invoice number and date.
As long as this text field does not exist, the generic text field before the list of invoice items could be used as a makeshift.
