You fasten the coat and your dog becomes a statue. They may dislike the pressure, the way it goes over their head, or a poor fit. Freezing is not proof they are getting used to it. Take it off and let them move normally.
Not every dog needs a coat. Ask your veterinarian if you are unsure what suits your dog's breed, coat, age, and health in your climate. If clothing rubs, restricts movement, or presses on a painful area, change the fit or the plan. Some dogs need warmth but do better with a different design.
Start with a coat on the floor
Let your dog inspect it while you offer treats, then put it away. Next time, lift the coat briefly and reward. If it must pass over the head, invite your dog to put their nose through the opening rather than pushing it onto them. Reward and let them back out. Add a moment of fabric resting on the shoulders only when they remain comfortable. Fastening and walking can be separate later steps.
Keep the first wear very short and watch for free movement, sniffing, and normal posture. If your dog freezes, pants, or tries to escape, remove it and make the next step easier. Practice inside before a cold, wet walk makes the coat feel urgent. If you need to go out today and the coat still worries them, choose a shorter safe trip or another weather solution.
A useful coat is one your dog can move in. There is no benefit in a perfectly dressed dog who cannot take a step. Once fit and possible pain are checked, the dog handling and reward-timing guide can help you time easy rewards as your dog chooses to investigate clothing. Skip the coat if it keeps them frozen.
Sources: Dogs Trust: How to get your dog used to wearing a coat. Dogs Trust: How to keep your dog safe and warm in cold weather.