How to write C# for barcode scanner to validate correct barcode and shows green light or beeping?

Some scanners have 2 modes, a proprietary format, and what's called a keyboard wedge. The easiest (and most portable) way is with the wedge. It's a driver that sends the characters scanned as if they were typed. Add a message filter to your app to pre-handle key presses, and when it detects a stream of characters in a timespan that no human can type, you've got the barcode.