If you use a script to duplicate the invoice, it can include this script step to clear a field whose data you do not want in the duplicated record:
Set Field [Imvoice::creditCardNumb ; "" ]
When I try to enter this in the Set Field step, it tells me that an operator is expected here and highlights ;""
When Setting up Set Field, there are two Specify buttons that must be clicked. To get Set Field [Table::Field ; Expression], add set field to your script and click the first button (specify target field). Select Table::Field from the list of fields. Click OK. Now click the lower specify button (calculated result) and create the expression to the right of the semicolon (;). Do not try to type in the semicolon.