The printer name for Zebra label printers such as the ZP 450 may have 2 consecutive spaces which can cause problems. Removing one of the spaces in the printer name should resolve the issue.
1. Go to Control Panel -> Devices and Printers. Right click on the Zebra Printer and select 'Printer Properties'.
2. Edit the printer name and remove one of the spaces between 'Zebra' and 'ZP'. Save.
3. Go back to the Shipping page in SupportSync. Refresh the page and run the Label Printer Setup again. Make sure that the new name of the printer is shown and select it.
Now you should be able to print to the Zebra printer.