This numpad connects to the keyboard through a USB-C port and two tiny magnets on each side of the port, nothing else. So the slight slip, accidental move or wrong handling can break the magnets and potentially the USB-C port, making the numpad useless on that side.
And do not attempt to fix it as it can make the other side stop working. I would not buy this unless they improve the design to something a lot more sturdy. Not worth the €50 price at all.
Also, the warranty does not cover this kind of damage, so only buy this if extremely necessary.