So I'm a retailer with many serialized products. Let say I have one product in stock, with a in stock quantity of 2 pieces. Each has a unique serial number, say "123" and the other is "456". When the product is sold in the PoS, the window to enter the serial number comes up. The employee can enter any number there, even a serial number we don't have, like "789". How do I restrict the serial numbers that can be entered to the ones defined already? Or better yet, get a dropdown of the ones available?