Why is customer relation number not available in Zoho Invoice?

Why is customer relation number not available in Zoho Invoice?

Hi Zoho Invoice,
 If you have 10 customers with the same last name, or even same first name, how do you quickly find the correct record?

Most CRM and Invoicing systems have a unique customer relation number assigned for each customer registered in the system.

Wny is this very simple but so important function not available in Zoho Invoice?

If a unique customer relation number is generated (auto numbering) each time you register a new customer, it will simplify the process of finding the right customer when you receive a phone call regarding a certain payment.

Furthermore, it will decrase the risk for mistakenly sending the wrong invoice to wrong customer.

So my questions is why isn't there a unique ID and does anyone know of a work-around for this problem?

No, answers such as "the email address it the unique factor that distinguish one customer from another." does not help us, since many of our customer do not have email addresses.

How soon can you implement this simple and very useful function?

Look forwards to receive your reply within soon.