Shift is invoiced
You will not be able to edit a shift if client's invoice has been generated from that shift. Shift is flagged blue in scheduler.
Once invoice is generated, it blocks the shift from further changes. If for any reason you want to make changes, then you need to void invoice. Click the sidebar menu heading Invoices, now click List. Find the invoice in question and click the void button.
The shift will now be available to edit again in scheduler.
Shift is cancelled
Cancelled shifts cannot be edited. Shift will be flagged yellow in scheduler.
In order to make changes in cancelled shift you have to rebook the shift. Click the shift you want to rebook, click More options. Now you can click Rebook and make the shift available again.