The opening is familiar, but the moving flap changes the task. It may touch your dog's head or back, swing noisily, or make the other side hard to see. Do not push the dog through or close the flap against them. They can use another supervised way in and out while you work on this.

Check the setup

Make sure the door is the right size and moves freely, with no sharp edge or pinch point. Keep both sides clear and secure. A pet door should not be the only way a dog can get outside for a necessary toilet break. If reluctance appears suddenly after comfortable use, check for damage to the flap or a painful change in the dog and ask your vet when appropriate.

With the flap held open, invite the dog to investigate from either side and reward voluntary movement. Then, on a later attempt, let them see or hear you move the flap gently without asking them to pass through. Only when they remain comfortable should the opening become a little less open. Let them back out at any point. If they freeze, retreat or stop taking a usual reward, make the next step easier. The goal is confident use, not a timetable.

Today, check the flap and reward one easy look or sniff while it stays safely open. That is progress even if your dog uses the ordinary door for the rest of the day.

Sources: AKC on teaching dogs to use a moving dog-door flap. VCA on recognizing fear and avoiding force.