Right now the merchant sends me an EMail each month with a very long URL that takes me to an invoice that I have to pay. If I don't get the EMail, I don't know how much I owe and I don't have a way to pay it. If you allowed me to create an account on your website, such that the merchant could add invoices to my account and I could log in to my account, see the invoices and pay the most recent one, things would be simpler for everyone. I could find and pay an invoice without hunting for an EMail with the very long URL.