An event with 150 attendees might, in our case, result in 50 payments in advance by credit card and 100 payments on event day by check or cash. Marking an invoice paid requires three screens, three clicks, so that means 300 screens to clear all the invoices from a single event (we have at least one event per month).

You give us an export function to export invoices; what would be handy is a similar import function so we could edit the XLS file and then import it back to clear the invoices.