I'd like the option to add a payment from the invoice listing page.
Some clients pay 2-3 invoices in one go. I'd like to be able to look at the list of invoices, tick the box on the left hand side, then have a icon top right (where assign project/print etc are) to mark as paid. A pop-up would come up, and you can mark them paid without having to open each individual invoice to pay.
A bonus feature would be totalling the figure of the ticked invoices. Sometimes i get paid 3 invoices out of 6 due, and it's not necessarily the oldest one that gets signed off and paid first. So it would be nice to see the total of the invoices ticked, so you can tick different combinations until you get to the amount they've paid in a lump sum.