Inventory - no field on package slips for the sales order reference number

Inventory - no field on package slips for the sales order reference number

This is about the sales order reference number (customer's purchase order number), not the sales order number.

We use Inventory for package slips - however there is no field for the sales order reference number (which is the customer purchase order number) - please add this to the package slip or the customer cannot match deliveries to orders. The field is in the sales order but not as an option to add to package slips.

There is the field in Zoho Books called reference number so why not in Inventory?  We cannot use the package slip in Books as it can only be selected after the invoice is created and we invoice after we ship the goods!!

The best place for it is in Inventory as this is what our warehouse uses. It is just a small but very important field.