Getting the Outstanding Trade Receivables of a Customer

Hi SAP Experts,

I am trying to make a report to show the outstanding trade receivables of a customer based on his payment terms. I have a few questions I want to ask to all of you:

1. Can a direct FI invoice for a customer be partially collected? If yes, how do I find the information of the outstanding value of that direct FI invoice?

2. How can I check the outstanding value of an invoice partially collected that is based on a Sales Order/Billing Document?

Thanks,

Josef