You have barely sat down when your dog starts scanning, whining, and pulling toward passing people. A cafe brings food, moving chairs, dogs, and strangers close together. If your dog cannot rest or take a treat, leave calmly rather than waiting for them to get used to it. A short outing that ends before a reaction is useful information, not failure.
Keep your dog on a secure lead and out of aisles, doorways, and servers' paths. Do not tie them to a lightweight chair or table. If they growl, snap, or cannot safely pass other dogs, choose a different setting and seek qualified, reward-based behavior help. A sudden change in tolerance also warrants a veterinary check.
Practice the easier version
Teach settling on a familiar mat at home. Reward a relaxed posture and gradually extend the time between rewards. Then practice in a quiet outdoor spot with room to leave, without ordering food or committing to stay. Keep sessions short and give your dog time to sniff before asking them to lie down. As it becomes easy, add one mild distraction at a time.
Choose a spacious cafe at an off-peak hour only when your dog can relax in other public places. Sit near an exit, bring water, and plan to leave if their body stiffens or they become fixated. Some dogs may never enjoy a busy cafe. You can still share other outings that suit them better. For more on taking an easy home skill into a new place, see the training in everyday settings guide, a busy café is optional and a short exit is a good choice
Sources: Dogs Trust: How to train your dog to be calm, relax and settle. Dogs Trust: Reactive dogs - why it happens and how to help.