Lol, poor Floppy. Maybe you could put a feather or something to attract them in the middle of the cat door. Just so they get the idea. Or open the cat door and put your hand through and pet him. Maybe he will get th hang of it.
Still waiting to see who'll be the first to have the epiphany that this is exactly the same as any other cat door they've gone through over the last 10 years. It just goes through a screen instead of on opaque piece of wood....