<button id="signin-sms">Login</button>

  <script src="//cdn.auth0.com/js/lock-passwordless-1.0.min.js"></script>
  <script type="text/javascript">
  
    document.getElementById('signin-sms').onclick = function () {
      var pwdless = new Auth0LockPasswordless('client-id', 'app-domain');
      pwdless.sms(function (err, profile, id_token) {
        // Passwordless Authentication handler    });} </script>