Has this happened to you?
The project isn't quite finished, but you want to submit your invoice because you know it will take a while to get your money or just because you're in the midst of a cash flow crunch.
I suggest saying something along the lines of, "We’re winding down and here’s what’s left to do: [list the details]. I’d like to get the final invoice into your system. Does that work on your end?”
When it comes to talking about money—the Creative Professional’s Guide to Money provides great language and guidance for a number of money-related situations.