There may be instances where administrators do not want agents adding to or modifying bookings once they have been invoiced.
Administrators are able to set this as part of their user permissions under Settings > Users.
Select the user you wish to edit, and from the Permissions tab, de-select the Edit Invoiced Bookings permission in the Bookings dropdown:
Once this has been set, the following notice will display above all Invoiced and Closed Bookings:
The following controls in the booking are also disabled at this point: