Excess or partial payment

What happen when a client pay more or less than the total amount of the invoice, currently there is no way to capture that kind of a transaction and it is crucial for that option to exist in the system as most customers pay diffrently based on their circumstances.

You can change to total as you when you add payment.

I have a same issue. Lets say I have raised three invoices of $100, $200 and $300. My client decides to pay $400, $100 and then $100. How do I enter this transaction?