Help getting my pug through the doogy door

Hey y'all. This is Louie and he's afraid to go through the doggy door. We've had the door in our home for ages and our other small dog uses it all the time. We adopted Louie a week or so ago and so far, he doesn't really get it.

If I put a treat inside there, he will grab it but only if I am holding the flaps up (like in this picture). As soon as the flaps come down, he acts like it's an impenetrable wall. He's seen his bro dog go through so many times but I guess it just hasn't clicked yet how he can push on the flaps to move them.

Looking for any tips and tricks you all might have used to get this process moving. This is Day 4 of him not learning. If the answer is just keep working with him, patiently, I'm good with that but hoping for other ideas if you have any. Cheers,