How can I add the Purchase Order number from the customer to the sales order or sales invoice?

Note: There is no specific field for the purchase order received from customer on the Sales Order or Sales Invoice.

Workaround:

1. Open the Sales Order or Sale Invoice window to create the transaction.
2. Enter the P.O. number received from customer in one of these options:
   • To the Message field 
   • On  the next line below the last transaction under the Item Description column.
   • You can also add it beside your Order number by separating them with a '-' or a '/'.