Dogs

Physically pushing Louie all the way through the door (without lifting the flaps first; like using Louie himself to push the flaps out of the way in a way that mimics how dogs would ordinarily do it) a few times a day couldn't hurt.

Also, if he's only been 4 days, it's likely he's kindof freaked out. It might be that as he acclimates, he'll naturally get the "confidence" to try it out himself.

Good! He'll take treats from the tunnel when you hold the flaps up. That's a huge start!

Boil some chicken and do the same treat thing you've been trying. Then, show him you have the chicken. Place some shredded boiled chicken into the tunnel and tell him to stay. Close the flaps and then tell him to get it. He'll likely whine and poke his little head against the flap. Give him 5-15 seconds before you help him by lifting the flap a tiny bit. More and more until he takes the chicken. Then, lift the flap less and less until he grabs it from the tunnel on his own. DON'T LET THE INNER FLAP CLOSE!!! Keep an eye on him to make sure he doesn't get his head stuck trying to step back from the tunnel. If he has real cause to freak out, you're gonna lose a lot of progress.

Got him eating from the tunnel? Awesome! Now leave him inside and go outside and call him out with you. He won't love it, but you'll have your secret weapon: shredded boiled chicken. Reach through the doggy door to show him you have this high value reward and then leave a BIG pile of it outside. If that doesn't encourage him to go through, have someone start giving him a little push through. When he accomplishes it, HIGH PITCHED HAPPY PRAISE! YAAAAAAAAAYYYYYYYY!!!! Lots of happy pets and scratches and play! Keep trying this, he should pretty quickly enjoy hopping out on his own pretty quickly.

Now, for the final step. Go outside with him. Go back inside without him. Call him in. Call your other dogs and offer them treats. Send them outside and call them back in, and then just hang out. If he starts barking, call him in. Don't help him. At some point, your new boi should magically appear inside the house and you'll be so excited for him that all the puppies get treats, YAAAAAAAAAYYYYYYYY!!!!!

At least, this is what worked for me when I installed the new through-wall dog door with the double sealing flaps. Then, I adopted another pound dog who'd never seen a doggy door before and whose veins flow with anxiety and cocaine.

Doogy

I am not an expert, but I think you have the right idea to just be patient. I am completely confident Louie will eventually figure it out himself! (Side note: Louie is the best, like every dog and I love him.)

One of our dogs was mentally disabled so it took him a few days to figure it out. Don’t give up just yet. It took some treats, which I noticed you’ve used as well, and some occasional re-teaching, but he used the flaps plenty.

Just remember that learning takes place after need and want are established. The first time he came inside through the doggy door was when he was given no other option. It was a pleasant day, so he was simply left outside for 20 minutes and watched as I ate popcorn in front of the door, occasionally offering it to him.

Bacon

Maybe put a transparent flap?

Tape the flap halfway or 3/4 up until he goes through it regularly. Then decrease the amount it's open until he's comfortable with it again and rinse/repeat until he gets it.

Takes some time and patience. Other posters have given tips on how to encourage the dog to go through, that helps also.

Poor little inbred guy.

Can you use a rope/string with some treat attached to it, and try to lure him in that way? The other thing would be to put his meal right by the flap a couple of times.