An outstanding session is a session which is not yet invoiced.
To display the list of sessions for a client, click on the Sessions area in a Clients profile page.
The list of sessions is displayed. The first and the second sessions are the two outstanding sessions because these two sessions are not yet Invoiced. The third session is marked Invoiced.
Go back to the profile page by clicking on Back.
Click on the Invoices area in the Clients profile.
Then click on this existing invoice.
This will display the session that was marked Invoiced in the list of sessions for this client.
Head to Back > Back to Profile
Click on the + in Invoices area.
This will select the outstanding sessions for a client.
Click on Save to create an Invoice; otherwise click on Back.