Select Settings and then Template design and settings

In the section Item settings tap on the Barcode Scanner to turn it on

Select Save

Navigate to Products and either create or edit an item

Select the barcode icon next to Item code

A window with your camera opens

If a message appears "Billdu would like to access the Camera" click OK

Scan the barcode - Billdu automatically reads the code

Now the number sequence of the barcode appears in the Item code

Select Save

Edit or create an invoice or other document

Add an item 

Click on "Choose from services, products, expenses" on the black bottom bar

Select the barcode icon in the upper right corner

A window with your camera opens

Scan the barcode

The app reads the code and adds the right item

Select Save to save the item to the invoice