Why can’t I add certain timesheets to my Invoice?

Ensure if the timesheet is associated with a Fixed Cost Project. If it is, such timesheets are considered Non-billable and cannot be individually included in an invoice. Instead, a single line item representing the entire project, along with its fixed cost, will be added to the invoice.

As a workaround, you can enter a note in the Notes section of each timesheet indicating that the time log has been invoiced. These details can be exported from the Timesheet Details report.