We’re are happy to tell you that we’ve managed to find a suitable provider and implement the solution on WHMCS.
To pay with credit card, just open your invoice on your client area, and select Credit Card (Stripe). You will need to enter your credit card information on our website, but do not worry about safety, since we do not save any credit card information ourselves (it will be saved only the last 4 digits and a Credit Card Token provided by Stripe).
Credit card payments are immediately validated, meaning that there won’t be any human interaction on this transaction.
Edit [02-05-2016]: due to an issue with HiPay, we cannot accept credit card payments anymore.
Edit [27 06 2016]: We are now accepting credit card payments through Stripe.
Thank you for your time