Invoice can be paid without having to be logged in to whmcs
Some customers want to send the invoice to friends or even a family member, the idea is that the invoice could be generated and through the link the customer would pay the invoice without needing the customer to be in their account. this would even facilitate sending the link via e-mail, so that the customer would not need to do the entire process of logging into the account. he was only going to pay the invoice through a "public" link. this link was going to be generated so he could make the payment.