If the 'OPOS' option was selected in the Printer field, you must enter the OPOS driver name for the printer here.
Both the Programmatic ID and the Logical Device Name can be used as the Device Name for the printer.
You can find the Programmatic ID and the Logical Device Name in the registry:
HKEY_LOCAL_MACHINE\SOFTWARE\OLEforRetail\ServiceOPOS\POSPrinter