Will he go in by himself during the day? Try shining a light inside the crate so the pup can see better, then toss the treat to the back of the crate. Dogs apparently have far better night vision than we do, but I've noticed sometimes dogs don't like to go into pitch dark spaces, or sometimes green agility dogs don't like the curved, dark colored tunnels because they can't see the end, just a black void. My own dog won't jump off the bed if the room is pitch black. Worth a shot, and if that doesn't work I would up the value of the nighttime treat, like a piece of hot dog or tiny piece of cheese.