Add Purchase Order(PO), Invoice, Customer Reference, and Department numbers
The code facilitates you to add the purchase order, invoice, customer reference, and department numbers on shipment label.
Add the following code to your functions.php or anywhere relevant.
In the above code, assign $po_number, $inv_number, and $customs_duties_payer as per requirement. Then, store all these numbers into $reff array. For all existing values, append $request with $reff and return $request.