Steps to follow

1. Expand the blue button (bottom right) click New invoice (or press ctrl i if you're on a desktop).
2. Select your date range and choose the relevant client.
3. Select the relevant appointments (if you look at the appointment information, you will notice that they specify which practitioners they saw).
4. Click Create invoice.

The invoice description for each appointment will contain something like: "Treated by {person} ({registration number}) at {location}".

Configure the default invoice description from Advanced Settings:

1. From the sidebar, under Spaces, click Settings.
2. Choose an option in the dropdown titled: Set a default invoice description on new appointments.

Note: these changes will only apply to new appointments.