Use Physical Keyboard

I tried to use different physical keyboards in the Klara app for my shop, but none of them works. Using the small digital numbers and buttons on the app display is a much slower process than typing it on a real keyboard, whether it is to finalize a purchase or for typing the total of a purchase. 

Is it a limitation of the Klara app, or is there a way to enable it?

On my understanding, the bar code scanner is recognized by android as a physical keyboard, so maybe the problem is related to this?