test.html

<head>
  <title>Checkout</title>
  <script src="https://js.monei.com/v2/monei.js"></script>
</head>
<body>
  <form
    id="payment-form"
    action="https://secure.monei.com/payments/3c591eec63a839ef4f21356b1c38c50832f9d1c2"
    method="GET"
  >
    <button id="payment-button" type="submit">Pay</button>
  </form>
  <script>
    const paymentForm = document.getElementById('payment-form');
    const paymentButton = document.getElementById('payment-button');
    paymentForm.addEventListener('submit', function (event) {
      event.preventDefault();
      paymentButton.disabled = true;
      monei
        .confirmPayment({paymentId: '3c591eec63a839ef4f21356b1c38c50832f9d1c2'})
        .then(function (result) {
          paymentButton.disabled = false;
          // At this moment you can show a customer the payment result
          // But you should always rely on the result passed to the callback endpoint on your server
          // to update the order status
          console.log(result);
          if (result.status === 'SUCCEEDED') {
            handleResult(result);
          } else {
            handleError(result);
          }
        })
        .catch(function (error) {
          paymentButton.disabled = false;
          console.log(error);
        });
    });
  </script>
</body>