Sorry, but the payment service is a bit confusing. To pay by VISA or Mastercard, you first need to click the PayPal option, then click "pay with card" or "checkout as guest" (no need to create a PayPal account).
- Click PayPal > Continue to PayPal

- Click "Pay with a card" or "Checkout as guest" (text may vary, depending on location)

- Pay by credit card, via PayPal

Process with screenshots above, in case anyone else has the same issue. As noted, this payment service is a bit confusing, but I'm currently stuck with them. As stated on the initial payment page "All Visa/Mastercard/Diners/Amex payments are being processed via PayPal: either using a PayPal account or checking out as a guest with the “Pay with Debit or Credit Card” option".
Sorry for any inconvenience 🙏