To test if your using barcode number scanning in S5 and scanner is set up or configured in the system,

Open an invoice. If your scanner and S5 are not configured to work properly, you can still scan into the Part No field, it will still work properly. However, if you're able to barcode scan into the quantity field and it holds that quantity or see's that barcode number as a quantity. The system will give you an error saying that the number seems normally large for a quantity. 

To configure the scanner, we need to use the manual or download it from the internet. We need prefix or STX or Ctrl +B to work in S5. Either of these will work. We also need a carriage return or enter. 

To set this up, go to Setup Tools > Setup Wizard > Point of Sale Devices > Barcode Reader

If it's not setup as this (as shown in the picture above), just click on Default Pre-amble Setting then Save Settings.

To confirm that it's working properly, click the Read Barcode Scanner then scan an item. It should read the barcode appropriately and put it into the barcode field. That means that the scanner is setup or configured properly.  Please note that this is a setting that needs to be set on all the computers using a barcode scanner.