Due Date Questions

Hi
We worked with the whmcs demo tool for some time and wanted to use it in our hosting environment. We have nevertheless a few questions related to invoicing, products and due date.

*** Client Profile - Tab Product/Service ***

Next Due Date : what does this date represent ?

- when I create a product
- after 12month

in our case this date is always the same then registration date


*** client Profile - Invoice - Options***
- Invoice Date
- Due date

It's somehow confusing and documentation does not resolve on these fields

Regards