Pay invoice as a Guest (i.e., without using an e-mail address)

Pay invoice as a Guest (i.e., without using an e-mail address)

I am a physician and may of my clients are older and thus may not have an e-mail address or have not provided me with an e-mail address. Can I set up invoices to allow patients to sign on as a guest using an invoice number or patient unique identification number and a password (provided to the patient on the invoice) without having to supply an e-mail address with the option of setting up an account using their e-mail address? Many healthcare patient portals allow patients to sign on and pay invoices by just supplying their account number or invoice number and a password provided on the invoice.