You can easily change the status of "Invoice not issued" by clicking on it with the left mouse button. You will be able to enter the invoice number in the pop-up window and save the entry. The invoice number is optional, you can leave it blank.
Once saved, the status will change to "Invoice issued" and turn green. If you entered an invoice number in the blank field, it will be visible together with the date and time.
If you want to reset the invoice status, click the “Detailed view” option. Go to the "All actions" menu and choose the “Reset invoice status” option. It will update the work order and the invoice status will be changed to “Not billed” again.