You are able to pay with a Credit Card using PayPal, without having a PayPal account.
Follow these steps
1. Log into your client area using your credentials.
2. To the right you will see an "Invoices" link, click on that link.
3. You will now see a list of invoices, click on the unpaid invoice you would like to pay for.
4. You will be shown the detailed invoice, and to the right down the middle of the invoice you will see "Payment Method", choose PayPal/Visa.
5. At the very top you will see a yellow PayPal link, click on it to pay the Invoice.
6. You will be taken to the PayPal website, and will be able to pay for the Invoice by entering your Credit Card details.