To build your report please follow these simple steps:
1) Click on "Time Entries" at the top of the screen.
2) Make sure to change any of the filters to match the time entries you want to display and report.
3) Click on the three dots next to the column "Status" and then hit "Filter".
4) Change the fields in the filter to match the ones in the screenshot below.
What Happens Now?
Now you can see what has been billed previously and what still needs to be billed for a later time.
From this point you can generate invoices for the billable time that is available.