Billy Invoice management is the system for the management of unpaid invoices. a doctor has patients, the patients do not pay the bills. The doctor manages these invoices in this system in PDF or XML format. After x days, the doctor gets tired of waiting and following up so he sends us the invoices of some patients by creating an account and adding the invoices on our system, we see the invoices deposited and can assign them to a department or a person. Then the department or the person will contact the patient and make letters, e-mails, phone calls to arrange the payment.(The doctors were an example but it could be many other types-Bills from a mechanic, dentist)