If you want to Pay with American Express or Debit Card:
1. Choose payment method: Paypal. Continue even if you don't have Paypal.
2. You will be prompted to "Log In" or "Pay with Debit or Credit Card". Click "Pay with Debit or Credit Card".
(NOTE: If that button says Create an Account, then still click it, it will send you to Paypal Guest Checkout and you don't have to create an account.)
3. This will send you to Paypal Guest Checkout, this will not force you to create an account, you can simply enter your Credit Card details there:
4. Congratulations, it was that easy!