<script>

  const form = document.getElementById('myForm');

  const checkbox = document.getElementById('agreeCheckbox');

  const warningMessage = document.getElementById('warningMessage');

 

  form.addEventListener('submit', function (event) {

    if (!checkbox.checked) {

      event.preventDefault(); // Stop form submission

      warningMessage.style.display = 'block'; // Show warning

    } else {

      warningMessage.style.display = 'none'; // Hide warning

    }

  });

</script>