Good morning, I have something similar in my app. We made a billing feature so I have table labeled invoices. My project coordinators enter the dates of invoices to go out and amount and it shows what is left to bill. Each Monday my Project Accountant gets a list of what to invoice. The benefit of that is the billing is automated as long as amounts and dates are kept up to date.
i can use that for a monthly projection and I color code it via formula for invoices that were submitted so I know what went out.
i also enter paid information etc so my sales team can monitor without needing access to the accounting software.