The SaaS is for real estate companies, and they can pay a monthly fee that will offer them 1000 publications but they can also consume additional publications or other services that will appear on their bill as extras.

On registration the user can choose one of the 5 available plans that the only difference will be the quantity of publications their plan allows them to make. But they can pass that limit if they wish, and additional payment will be required on the next bill.

A publication means: Publishing a property during one day, for 1 whole month would be: 30 publications. And 5 properties during one day would be 5 publications.

So basically the user can:

• Make publications (already paid in the monthly fee, extra payment only if it passes the limit)
• Highlight that publication (extra payment)
• Publish on other websites or printed catalogues (extra payment)

Doubts:

• How to handle modifications in pricing plans? Let's say quantities change, or you want to offer some free stuff.
• How to handle unpaid invoices? I mean, freeze the service until the payment has been done and then resume it.
• When to make the invoices? The idea is to make one invoice for the monthly fee and a second invoice for the extra services that were consumed.
• What payment methods to use? The choosen now is by bank account, and mobile phone validation with a SMS. If user doesn't pay we call that phone and ask for payment.

Any examples on billing online services will be welcome! Thanks!