How do I link a purchase order (PO) number to a sample?

 When registering electronically in the portal, there is a dedicated field for the purchase order number. This ensures correct labelling on the invoice.

Alternatively, if you use the paper form, there is a dedicated field there: Purchase order number

The Work order number field is typically the job number in your own systems, which will appear on reports and on the invoice line item, but it must not be confused with the purchase order number.