Hi. The button will not just send data by itself. You need to pair and initiate transmission first.
I suggest you to look at our protocol specification at https://github.com/50ButtonsEach/flic2-documentation.
If you can't use the flic2lib-android directly, you can at least look at the source code at https://github.com/50ButtonsEach/flic2lib-android/blob/master/flic2lib-android/src/main/java/io/flic/flic2libandroid/Flic2Button.java and try to port it to C#. The code follows the protocol specification.