'You are not allowed to use Docker, you must be in the "docker-users" group'. What should I do?

It means that you are on Windows.
  • Search and open 'Computer management':
  • Go to 'Local users and groups':
  • In 'Groups', double-click 'docker-users':
  • If you are not in 'docker-users', go to 'Users' on the left filter and add you in the 'docker-users' group by clicking on you and 'Add...':