I'm so close to a solution. It is probably an easy fix - I've just hit coding writer's block.
I created a spreadsheet that when the user changes the invoice number, it automagically populates the list of tasks used in that invoice period with this array formula:
It works great on Invoice 1, but when I switch to Invoice 2, it doesn't work. I know why. This part of the code (Task!$D$6:$D$11) needs to vary when I change from Invoice 1 to 2 or 3. I could do a switch formula, but I'm hoping there is a more elegant solution. Maybe nesting another match formula? Here's where I need your help!
I have attached the file to help you visualize what I'm doing. Any help is appreciated!