If clicked, the invoices with their reason codes and date and time stamp will be recorded in the Non_Payment_Invoices table.  

When a supplier has been selected this grid will populate with unsettled and partially settled invoices.  You may select invoices and add non payment reason codes for it.

This is the supplier invoicing your company.   It is populated with the supplier name, code, status, and clerk from the External Organisation table where the supplier has a valid creditors account.

The number of characters to be entered before the list is shown is governed by the value of "populate length" (mandatory).